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C programming session8

Bit-fields allow access to individual bits within registers or bytes. They define the number of bits allocated to each field within a structure. Pointers store the address of other variables in memory and can be used to access or modify these variables indirectly. Pointer arithmetic allows pointers to be incremented or decremented to access sequential memory locations represented by an array.

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Overview of C Programming, highlighting key issues such as accessing wrong bits on registers for embedded programming.

Explains bit-fields in C, their purpose, struct definitions, and examples. Discusses limitations and practical applications in embedded systems.

Introduces pointers, explaining their definition, utility, and declaration in C programming.

Details on pointer declaration, types, and implications of using pointers effectively in C.

Discusses the basic arithmetic operations applicable to pointers, focusing on addition and subtraction only.

Establishes the close correlation between pointers and arrays, providing examples of syntax and usage.

Elaborates on how pointers interact with functions, enhancing data transfer and enabling multiple outputs.

Defines void pointers, their use cases, and significance in passing different types of data.

Explains multiple indirection in pointers, addressing risks associated with unassigned pointers.

Showcases practical application of pointers in hardware communication with UART, including function calls and interrupts.

Introduces the concept of 'const' in C programming to define unmodifiable pointers or values.

Discusses various types of constant pointers in C, emphasizing their applications and examples for clarity.

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C_Programming Part 8 ENG. KEROLES SHENOUDA 1
Access Wrong Bit on the Register one of the most famous issue for the embedded programmer 2 Functionality issue
Bit-Fields THINK FIRST THEN ANSWER HOW TO USE STRUCTURE ON ACCESS SPECIFIC BIT ON THE REGISTERS ? 3
Bit-Fields  Unlike some other computer languages, C has a built-in feature, called a bit-field, that allows you to access a single bit. Bit-fields can be useful for a number of reasons, such as:  If storage is limited, you can store several Boolean (true/false) variables in one byte.  Certain devices transmit status information encoded into one or more bits within a byte  Certain encryption routines need to access the bits within a byte. 4
Bit-Fields  A bit-field must be a member of a structure or union. It defines how long, in bits, the field is to be. The general form of a bit-field definition is type name: length;  type is the type of the bit-field, and length is the number of bits in the field. The type of a bitfield must be int, signed, or unsigned. (C99 also allows a bit-field to be of type _Bool.)  Bit-fields are frequently used when analyzing input from a hardware device. 5
Bit-Fields For example, the status port of a serial communications adapter might return a status byte organized like this: Bit Meaning When Set 0 Change in clear-to-send line 1 Change in data-set-ready 2 Trailing edge detected 3 Change in receive line 4 Clear-to-send 5 Data-set-ready 6 Telephone ringing 7 Received signal 6 struct status_type { unsigned char delta_cts:1; unsigned char delta_dsr:1; unsigned char tr_edge:1; unsigned char delta_rec:1; unsigned char cts:1; unsigned char dsr:1; unsigned char ring:1; unsigned char rec_line:1; } status;
Bit-Fields  You might use statements like the ones shown here to enable a program to determine when it can send or receive data: 7 status = get_port_status(); if(status.cts) printf("clear to send"); if(status.dsr) printf("data ready"); Bit Meaning When Set 0 Change in clear-to-send line 1 Change in data-set-ready 2 Trailing edge detected 3 Change in receive line 4 Clear-to-send 5 Data-set-ready 6 Telephone ringing 7 Received signal struct status_type { unsigned char delta_cts:1; unsigned char delta_dsr:1; unsigned char tr_edge:1; unsigned char delta_rec:1; unsigned char cts:1; unsigned char dsr:1; unsigned char ring:1; unsigned char rec_line:1; } status;
What is the Output ? 8
What is the Output ? 9
Bit-Fields 10 struct status_type { unsigned char delta_cts:1; unsigned char delta_dsr:1; unsigned char tr_edge:1; unsigned char delta_rec:1; unsigned char cts:1; unsigned char dsr:1; unsigned char ring:1; unsigned char rec_line:1; } status; status 7 6 5 4 3 2 1 0 delta_cts delta_dsr tr_edge delta_rec cts dsr rec_line
Bit-Fields  You do not have to name each bit-field. This makes it easy to reach the bit you want, bypassing unused ones.  For example, if you only care about the cts and dsr bits, you could declare the status_type structure like this:  Also, notice that the bits after dsr do not need to be specified if they are not used. 11 status 7 6 5 4 3 2 1 0 cts dsr
Bit-Fields  It is valid to mix normal structure members with bit-fields. For example 12 What is the Output ?
Bit-Fields  It is valid to mix normal structure members with bit-fields. For example 13 What is the Output ?
Bit-Fields Bit-fields have certain restrictions  you cannot take the address of a bit-field. Bit-fields cannot be arrayed.  You cannot know, from machine to machine, whether the fields will run from right to left or from left to right; have some machine dependencies 14
Pointers 15
What Are Pointers?  A pointer is a variable that holds a memory address.  This address is the location of another object (typically another variable) in memory. For example, if one variable contains the address of another variable, the first variable is said to point to the second. 16
Why do we need Pointer?  Simply because it’s there!  It is used in some circumstances in C Remember this? scanf(“%d”, &i);
Pointers Pointer Variables  If a variable is going to be a pointer, it must be declared as such. A pointer declaration consists of a base type, an *, and the variable name. The general form for declaring a pointer variable is type *name; 18
Pointers Pointer Variables 19
Pointers Pointer Variables 20
Pointers Pointer Variables 21
Pointers Pointer Variables 22
23 What is the Output ?
Pointers Pointer Variables 24
Pointer Arithmetic  There are only two arithmetic operations that you can use on pointers: addition and subtraction. 25
26 rule govern pointer arithmetic.
All pointer arithmetic is relative to its base type (assume 2-byte integers) 27
Pointer to Array 28
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LAB Average of Weights  It is required to calculate the summation weight of 5 boxes. The user should enter the boxes 30
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Pointers and Arrays  There is a close relationship between pointers and arrays.  Consider this program fragment: char str[80], *p1; p1 = str; Here, p1 has been set to the address of the first array element in str.  To access the fifth element in str, you could write str[4] or *(p1+4) 33
Pointer to Structure 34 ->
Pointer to Structure 35
Pointers AND Functions  Pointers are used efficiently with functions. Using pointers provides two main features: Fast data transfer, because only pointers are transferred. Pointers allow the definition of several outputs for the same function. 36
Fast Data Transfer Using Pointers 37
Fast Data Transfer Using Pointers 38
Passing Arrays and Pointers to Functions Normal Array Passing 39
Passing Arrays and Pointers to Functions Array Passing with Pointers 40
Method 2 is completely equivelent to Method 1 which means that: 41
Finally we can summarize function parameters types  1. Input Parameters (Calling by Value) The parameter values is completely transmitted to the function. This gives the function the ability to read the transmitted data only. 2. Input/Output Parameters (Refrence or Pointer) The parameter pointer (refernce) is transmitted only. This gives the function the ability to read from and write to the original parameters. 3. Output Parameters (Return Value) The return data of the function is assumed as an output parameter. Normally C does not provide other Output parameters except the return value. 42
The sort function contains the two types of parameters. 43
Pointer with Unknown Type (void*)  Programmer can define general pointer without specifying a linked data type.  This type of pointers called (void pointer).  void pointer can not be used normally to manipulated data, it is required to type cast each data access operation. 44
Example: Universal Compare with void Pointers 45
Example: Universal Compare with void Pointers 46
The function prototype is:  int Compare(void* value1, void* value2, int type) which means it takes any two pointers with uncknown type, the third parameter informs the type of the submitted values (1 means integer, 2 means double). 47
Pointer Conversions void * pointers  In C, it is permissible to assign a void * pointer to any other type of pointer. It is also permissible to assign any other type of pointer to a void * pointer. A void * pointer is called a generic pointer.  The void * pointer is used to specify a pointer whose base type is unknown.  The void * type allows a function to specify a parameter that is capable of receiving any type of pointer argument without reporting a type mismatch.  It is also used to refer to raw memory (such as that returned by the malloc( ) function described later in this chapter) 48
Multiple Indirection Pointer to Pointer  You can have a pointer point to another pointer that points to the target value.  This situation is called multiple indirection, or pointers to pointers 49
Using Pointer to Pointer 50
Using Pointer to Pointer 51
NULL and Unassigned Pointers  If the pointer is unassigned it will contain an invalid address, it is unsafe to use an unassigned pointer, normally the program will crash. Fllowing program will crash because the (pX) pointer is not pointed to a valid address, it contain a memory gurbage 52
NULL and Unassigned Pointers  To avoid using unassigned pointers, all pointers must hold a valid address, if not it must hold a zero value. Sometimes zero value called (NULL). Above program may be fixed as shown bellow: 53
Labs 54
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10
An Illustration int i = 5, j = 10; int *ptr; /* declare a pointer-to-integer variable */ int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10 ptr int * integer pointer variable
An Illustration int i = 5, j = 10; int *ptr; int **pptr; /* declare a pointer-to-pointer-to-integer variable */ ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10 ptr int * integer pointer variable pptr int ** integer pointer pointer variable Double Indirection
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; /* store address-of i to ptr */ pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable *ptr int de-reference of ptr 5
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; /* store address-of ptr to pptr */ *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr *pptr int * de-reference of pptr value of ptr (address of i)
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 3 j int integer variable 10 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr *ptr int de-reference of ptr 3
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 7 j int integer variable 10 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr **pptr int de-reference of de-reference of pptr 7
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 7 j int integer variable 10 ptr int * integer pointer variable address of j pptr int ** integer pointer pointer variable address of ptr *ptr int de-reference of ptr 10
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 7 j int integer variable 9 ptr int * integer pointer variable address of j pptr int ** integer pointer pointer variable address of ptr **pptr int de-reference of de-reference of pptr 9
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 7 j int integer variable 9 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr *pptr int * de-reference of pptr value of ptr (address of i)
An Illustration int i = 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable -2 j int integer variable 9 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr *ptr int de-reference of ptr -2
Pointer Arithmetic  What’s ptr + 1?  The next memory location!  What’s ptr - 1?  The previous memory location!  What’s ptr * 2 and ptr / 2?  Invalid operations!!!
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) ? a[3] float float array element (variable) ? ptr float * float pointer variable *ptr float de-reference of float pointer variable ?
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) ? a[3] float float array element (variable) ? ptr float * float pointer variable address of a[2] *ptr float de-reference of float pointer variable ?
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) ? ptr float * float pointer variable address of a[2] *ptr float de-reference of float pointer variable 3.14
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) ? ptr float * float pointer variable address of a[3] *ptr float de-reference of float pointer variable ?
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[3] *ptr float de-reference of float pointer variable 9.0
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[0] *ptr float de-reference of float pointer variable ?
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) 6.0 a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[0] *ptr float de-reference of float pointer variable 6.0
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) 6.0 a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[2] *ptr float de-reference of float pointer variable 3.14
Pointer Arithmetic and Array float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) 6.0 a[1] float float array element (variable) ? a[2] float float array element (variable) 7.0 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[2] *ptr float de-reference of float pointer variable 7.0
Pointer to Function  powerful feature of C is the function pointer.  A function has a physical location in memory that can be assigned to a pointer.  This address is the entry point of the function and it is the address used when the function is called.  Once a pointer points to a function, the function can be called through that pointer.  Function pointers also allow functions to be passed as arguments to other functions 76
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Pointers Tricks 80 How to Read C complex pointer double to integer Modularity Pointer with Constant
How to Read C complex pointer expression Operator Precedence Associative (),[] 1 Left to Right *,Identifier 2 Right to Left Data Type 3 – 81 Before We Learn How to Read Complex Array we should first know precedence and associative . •Priority : Operator precedence describes the order in which C reads expressions •order : Order operators of equal precedence in an expression are applied Before Reading Article You Should know Precedence and Associative Table
How to Read C complex pointer expression 82
How to Read C complex pointer expression  char (* ptr)[5] Step 1 : •Observe Above Precedence Table •[] and () have Same Priority •Using Associativity , Highest Priority Element is decided •Associativity is from Left to Right First Priority is Given to “()” 83
How to Read C complex pointer expression 84 Step 2 : •Between Pair of Brackets again we have to decide which one has highest priority ? ‘*’ or ‘ptr’ ? •* and Identifier ptr have Same Priority •Associativity is from Right to Left First Priority is Given to “ptr”
How to Read C complex pointer expression 85 Read it as – ptr is pointer to a one dimensional array having size five which can store data of type char
How to Read C complex pointer expression examples 86
How to Read C complex pointer expression examples 87
How to Read C complex pointer expression examples 88
How to Read C complex pointer expression examples 89
How to Read C complex pointer expression examples  Test Your self 90
Pointers Tricks 91 How to Read C complex pointer Pointers on Embedded C Modularity Pointer with Constant
Pointers on Embedded C 92
93What is the Output ?
94What is the Output ?
Pointers Tricks 95 How to Read C complex pointer Pointers on Embedded C Modularity Pointer with Constant
Modularity 96
For example “UART” (send data)  Send_data(u16 data)  {  USART_Init ();  USART_Trans_Int_Enable();  USART_Trans_Enable();  USART_Transmit(u16 data);  } 97 USART_Init (){…} USART_Trans_Int_Enable (){…}USART_Trans_Enable (){…} USART_Transmit(u16 data); {…} UART
For example “UART” (send data)  Send_data(u16 data)  {  USART_Init ();  USART_Trans_Int_Enable();  USART_Trans_Enable();  USART_Transmit(u16 data);  } 98 USART_Init (){…} USART_Trans_Int_Enable (){…}USART_Trans_Enable (){…} USART_Transmit(u16 data); {…} UARTSend dataByte Byte Once the UART sent the Data, The TX interrupt will insert and the CPU will call ISR(USART_TXC_vect) { …….. }
For example “UART” (send data)  Send_data(u16 data)  {  USART_Init ();  USART_Trans_Int_Enable();  USART_Trans_Enable();  USART_Transmit(u16 data);  } 99 USART_Init (){…} USART_Trans_Int_Enable (){…}USART_Trans_Enable (){…} USART_Transmit(u16 data); {…} UARTSend dataByte Byte Once the UART sent the Data, The TX interrupt will insert and the CPU will call ISR(USART_TXC_vect) { …….. }
100 void (*Ptr_To_Trans_Int) (void); extern void USART_callback_Trans_Int(void (*Ptr_to_Func)(void)) { Ptr_To_Trans_Int = Ptr_to_Func; } USART_Init (){…} ISR(USART_TXC_vect) { …….. } ISR(USART_TXC_vect) { (*Ptr_To_Trans_Int)(); } UARTSend dataByte Byte
Pointers Tricks 101 How to Read C complex pointer Pointers on Embedded C Modularity Pointer with Constant
Variable Quantifiers - const  const is used with a datatype declaration or definition to specify an unchanging value  const objects may not be changed 102
Variable Quantifiers - const  const is used with a datatype declaration or definition to specify an unchanging value  const objects may not be changed 103
Constant with pointer 104
Constant with pointer 105
Complete the table yes/no … 106
107 int* ptr = &a; int* const ptr = &a; int const *ptr = &a; const int *ptr = &a;
Complete the table yes/no … 108 Try Now
Complete the table yes/no … 109
110
References 111  C The Complete Reference 4th Ed Herbert Schildt  A Tutorial on Data Representation  std::printf, std::fprintf, std::sprintf, std::snprintf…..  C Programming for Engineers, Dr. Mohamed Sobh  C programming expert.  fresh2refresh.com/c-programming  C programming Interview questions and answers  C – Preprocessor directives  Constant Pointers and Pointers to Constant A Subtle Difference in C Programming

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C programming session8

  • 1.
  • 2.
    Access Wrong Biton the Register one of the most famous issue for the embedded programmer 2 Functionality issue
  • 3.
    Bit-Fields THINK FIRST THENANSWER HOW TO USE STRUCTURE ON ACCESS SPECIFIC BIT ON THE REGISTERS ? 3
  • 4.
    Bit-Fields  Unlike someother computer languages, C has a built-in feature, called a bit-field, that allows you to access a single bit. Bit-fields can be useful for a number of reasons, such as:  If storage is limited, you can store several Boolean (true/false) variables in one byte.  Certain devices transmit status information encoded into one or more bits within a byte  Certain encryption routines need to access the bits within a byte. 4
  • 5.
    Bit-Fields  A bit-fieldmust be a member of a structure or union. It defines how long, in bits, the field is to be. The general form of a bit-field definition is type name: length;  type is the type of the bit-field, and length is the number of bits in the field. The type of a bitfield must be int, signed, or unsigned. (C99 also allows a bit-field to be of type _Bool.)  Bit-fields are frequently used when analyzing input from a hardware device. 5
  • 6.
    Bit-Fields For example, thestatus port of a serial communications adapter might return a status byte organized like this: Bit Meaning When Set 0 Change in clear-to-send line 1 Change in data-set-ready 2 Trailing edge detected 3 Change in receive line 4 Clear-to-send 5 Data-set-ready 6 Telephone ringing 7 Received signal 6 struct status_type { unsigned char delta_cts:1; unsigned char delta_dsr:1; unsigned char tr_edge:1; unsigned char delta_rec:1; unsigned char cts:1; unsigned char dsr:1; unsigned char ring:1; unsigned char rec_line:1; } status;
  • 7.
    Bit-Fields  You mightuse statements like the ones shown here to enable a program to determine when it can send or receive data: 7 status = get_port_status(); if(status.cts) printf("clear to send"); if(status.dsr) printf("data ready"); Bit Meaning When Set 0 Change in clear-to-send line 1 Change in data-set-ready 2 Trailing edge detected 3 Change in receive line 4 Clear-to-send 5 Data-set-ready 6 Telephone ringing 7 Received signal struct status_type { unsigned char delta_cts:1; unsigned char delta_dsr:1; unsigned char tr_edge:1; unsigned char delta_rec:1; unsigned char cts:1; unsigned char dsr:1; unsigned char ring:1; unsigned char rec_line:1; } status;
  • 8.
    What is theOutput ? 8
  • 9.
    What is theOutput ? 9
  • 10.
    Bit-Fields 10 struct status_type{ unsigned char delta_cts:1; unsigned char delta_dsr:1; unsigned char tr_edge:1; unsigned char delta_rec:1; unsigned char cts:1; unsigned char dsr:1; unsigned char ring:1; unsigned char rec_line:1; } status; status 7 6 5 4 3 2 1 0 delta_cts delta_dsr tr_edge delta_rec cts dsr rec_line
  • 11.
    Bit-Fields  You donot have to name each bit-field. This makes it easy to reach the bit you want, bypassing unused ones.  For example, if you only care about the cts and dsr bits, you could declare the status_type structure like this:  Also, notice that the bits after dsr do not need to be specified if they are not used. 11 status 7 6 5 4 3 2 1 0 cts dsr
  • 12.
    Bit-Fields  It isvalid to mix normal structure members with bit-fields. For example 12 What is the Output ?
  • 13.
    Bit-Fields  It isvalid to mix normal structure members with bit-fields. For example 13 What is the Output ?
  • 14.
    Bit-Fields Bit-fields have certainrestrictions  you cannot take the address of a bit-field. Bit-fields cannot be arrayed.  You cannot know, from machine to machine, whether the fields will run from right to left or from left to right; have some machine dependencies 14
  • 15.
  • 16.
    What Are Pointers? A pointer is a variable that holds a memory address.  This address is the location of another object (typically another variable) in memory. For example, if one variable contains the address of another variable, the first variable is said to point to the second. 16
  • 17.
    Why do weneed Pointer?  Simply because it’s there!  It is used in some circumstances in C Remember this? scanf(“%d”, &i);
  • 18.
    Pointers Pointer Variables  Ifa variable is going to be a pointer, it must be declared as such. A pointer declaration consists of a base type, an *, and the variable name. The general form for declaring a pointer variable is type *name; 18
  • 19.
  • 20.
  • 21.
  • 22.
  • 23.
  • 24.
  • 25.
    Pointer Arithmetic  Thereare only two arithmetic operations that you can use on pointers: addition and subtraction. 25
  • 26.
  • 27.
    All pointer arithmeticis relative to its base type (assume 2-byte integers) 27
  • 28.
  • 29.
  • 30.
    LAB Average ofWeights  It is required to calculate the summation weight of 5 boxes. The user should enter the boxes 30
  • 31.
  • 32.
  • 33.
    Pointers and Arrays There is a close relationship between pointers and arrays.  Consider this program fragment: char str[80], *p1; p1 = str; Here, p1 has been set to the address of the first array element in str.  To access the fifth element in str, you could write str[4] or *(p1+4) 33
  • 34.
  • 35.
  • 36.
    Pointers AND Functions Pointers are used efficiently with functions. Using pointers provides two main features: Fast data transfer, because only pointers are transferred. Pointers allow the definition of several outputs for the same function. 36
  • 37.
  • 38.
  • 39.
  • 40.
  • 41.
    Method 2 iscompletely equivelent to Method 1 which means that: 41
  • 42.
    Finally we cansummarize function parameters types  1. Input Parameters (Calling by Value) The parameter values is completely transmitted to the function. This gives the function the ability to read the transmitted data only. 2. Input/Output Parameters (Refrence or Pointer) The parameter pointer (refernce) is transmitted only. This gives the function the ability to read from and write to the original parameters. 3. Output Parameters (Return Value) The return data of the function is assumed as an output parameter. Normally C does not provide other Output parameters except the return value. 42
  • 43.
    The sort functioncontains the two types of parameters. 43
  • 44.
    Pointer with UnknownType (void*)  Programmer can define general pointer without specifying a linked data type.  This type of pointers called (void pointer).  void pointer can not be used normally to manipulated data, it is required to type cast each data access operation. 44
  • 45.
    Example: Universal Comparewith void Pointers 45
  • 46.
    Example: Universal Comparewith void Pointers 46
  • 47.
    The function prototypeis:  int Compare(void* value1, void* value2, int type) which means it takes any two pointers with uncknown type, the third parameter informs the type of the submitted values (1 means integer, 2 means double). 47
  • 48.
    Pointer Conversions void *pointers  In C, it is permissible to assign a void * pointer to any other type of pointer. It is also permissible to assign any other type of pointer to a void * pointer. A void * pointer is called a generic pointer.  The void * pointer is used to specify a pointer whose base type is unknown.  The void * type allows a function to specify a parameter that is capable of receiving any type of pointer argument without reporting a type mismatch.  It is also used to refer to raw memory (such as that returned by the malloc( ) function described later in this chapter) 48
  • 49.
    Multiple Indirection Pointer toPointer  You can have a pointer point to another pointer that points to the target value.  This situation is called multiple indirection, or pointers to pointers 49
  • 50.
    Using Pointer toPointer 50
  • 51.
    Using Pointer toPointer 51
  • 52.
    NULL and UnassignedPointers  If the pointer is unassigned it will contain an invalid address, it is unsafe to use an unassigned pointer, normally the program will crash. Fllowing program will crash because the (pX) pointer is not pointed to a valid address, it contain a memory gurbage 52
  • 53.
    NULL and UnassignedPointers  To avoid using unassigned pointers, all pointers must hold a valid address, if not it must hold a zero value. Sometimes zero value called (NULL). Above program may be fixed as shown bellow: 53
  • 54.
  • 55.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10
  • 56.
    An Illustration int i= 5, j = 10; int *ptr; /* declare a pointer-to-integer variable */ int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10 ptr int * integer pointer variable
  • 57.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; /* declare a pointer-to-pointer-to-integer variable */ ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10 ptr int * integer pointer variable pptr int ** integer pointer pointer variable Double Indirection
  • 58.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; /* store address-of i to ptr */ pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable *ptr int de-reference of ptr 5
  • 59.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; /* store address-of ptr to pptr */ *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 5 j int integer variable 10 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr *pptr int * de-reference of pptr value of ptr (address of i)
  • 60.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 3 j int integer variable 10 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr *ptr int de-reference of ptr 3
  • 61.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 7 j int integer variable 10 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr **pptr int de-reference of de-reference of pptr 7
  • 62.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 7 j int integer variable 10 ptr int * integer pointer variable address of j pptr int ** integer pointer pointer variable address of ptr *ptr int de-reference of ptr 10
  • 63.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 7 j int integer variable 9 ptr int * integer pointer variable address of j pptr int ** integer pointer pointer variable address of ptr **pptr int de-reference of de-reference of pptr 9
  • 64.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable 7 j int integer variable 9 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr *pptr int * de-reference of pptr value of ptr (address of i)
  • 65.
    An Illustration int i= 5, j = 10; int *ptr; int **pptr; ptr = &i; pptr = &ptr; *ptr = 3; **pptr = 7; ptr = &j; **pptr = 9; *pptr = &i; *ptr = -2; Data Table Name Type Description Value i int integer variable -2 j int integer variable 9 ptr int * integer pointer variable address of i pptr int ** integer pointer pointer variable address of ptr *ptr int de-reference of ptr -2
  • 66.
    Pointer Arithmetic  What’sptr + 1?  The next memory location!  What’s ptr - 1?  The previous memory location!  What’s ptr * 2 and ptr / 2?  Invalid operations!!!
  • 67.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) ? a[3] float float array element (variable) ? ptr float * float pointer variable *ptr float de-reference of float pointer variable ?
  • 68.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) ? a[3] float float array element (variable) ? ptr float * float pointer variable address of a[2] *ptr float de-reference of float pointer variable ?
  • 69.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) ? ptr float * float pointer variable address of a[2] *ptr float de-reference of float pointer variable 3.14
  • 70.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) ? ptr float * float pointer variable address of a[3] *ptr float de-reference of float pointer variable ?
  • 71.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[3] *ptr float de-reference of float pointer variable 9.0
  • 72.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) ? a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[0] *ptr float de-reference of float pointer variable ?
  • 73.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) 6.0 a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[0] *ptr float de-reference of float pointer variable 6.0
  • 74.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) 6.0 a[1] float float array element (variable) ? a[2] float float array element (variable) 3.14 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[2] *ptr float de-reference of float pointer variable 3.14
  • 75.
    Pointer Arithmetic andArray float a[4]; float *ptr; ptr = &(a[2]); *ptr = 3.14; ptr++; *ptr = 9.0; ptr = ptr - 3; *ptr = 6.0; ptr += 2; *ptr = 7.0; Data Table Name Type Description Value a[0] float float array element (variable) 6.0 a[1] float float array element (variable) ? a[2] float float array element (variable) 7.0 a[3] float float array element (variable) 9.0 ptr float * float pointer variable address of a[2] *ptr float de-reference of float pointer variable 7.0
  • 76.
    Pointer to Function powerful feature of C is the function pointer.  A function has a physical location in memory that can be assigned to a pointer.  This address is the entry point of the function and it is the address used when the function is called.  Once a pointer points to a function, the function can be called through that pointer.  Function pointers also allow functions to be passed as arguments to other functions 76
  • 77.
  • 78.
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  • 80.
    Pointers Tricks 80 How toRead C complex pointer double to integer Modularity Pointer with Constant
  • 81.
    How to ReadC complex pointer expression Operator Precedence Associative (),[] 1 Left to Right *,Identifier 2 Right to Left Data Type 3 – 81 Before We Learn How to Read Complex Array we should first know precedence and associative . •Priority : Operator precedence describes the order in which C reads expressions •order : Order operators of equal precedence in an expression are applied Before Reading Article You Should know Precedence and Associative Table
  • 82.
    How to ReadC complex pointer expression 82
  • 83.
    How to ReadC complex pointer expression  char (* ptr)[5] Step 1 : •Observe Above Precedence Table •[] and () have Same Priority •Using Associativity , Highest Priority Element is decided •Associativity is from Left to Right First Priority is Given to “()” 83
  • 84.
    How to ReadC complex pointer expression 84 Step 2 : •Between Pair of Brackets again we have to decide which one has highest priority ? ‘*’ or ‘ptr’ ? •* and Identifier ptr have Same Priority •Associativity is from Right to Left First Priority is Given to “ptr”
  • 85.
    How to ReadC complex pointer expression 85 Read it as – ptr is pointer to a one dimensional array having size five which can store data of type char
  • 86.
    How to ReadC complex pointer expression examples 86
  • 87.
    How to ReadC complex pointer expression examples 87
  • 88.
    How to ReadC complex pointer expression examples 88
  • 89.
    How to ReadC complex pointer expression examples 89
  • 90.
    How to ReadC complex pointer expression examples  Test Your self 90
  • 91.
    Pointers Tricks 91 How toRead C complex pointer Pointers on Embedded C Modularity Pointer with Constant
  • 92.
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  • 94.
  • 95.
    Pointers Tricks 95 How toRead C complex pointer Pointers on Embedded C Modularity Pointer with Constant
  • 96.
  • 97.
    For example “UART”(send data)  Send_data(u16 data)  {  USART_Init ();  USART_Trans_Int_Enable();  USART_Trans_Enable();  USART_Transmit(u16 data);  } 97 USART_Init (){…} USART_Trans_Int_Enable (){…}USART_Trans_Enable (){…} USART_Transmit(u16 data); {…} UART
  • 98.
    For example “UART”(send data)  Send_data(u16 data)  {  USART_Init ();  USART_Trans_Int_Enable();  USART_Trans_Enable();  USART_Transmit(u16 data);  } 98 USART_Init (){…} USART_Trans_Int_Enable (){…}USART_Trans_Enable (){…} USART_Transmit(u16 data); {…} UARTSend dataByte Byte Once the UART sent the Data, The TX interrupt will insert and the CPU will call ISR(USART_TXC_vect) { …….. }
  • 99.
    For example “UART”(send data)  Send_data(u16 data)  {  USART_Init ();  USART_Trans_Int_Enable();  USART_Trans_Enable();  USART_Transmit(u16 data);  } 99 USART_Init (){…} USART_Trans_Int_Enable (){…}USART_Trans_Enable (){…} USART_Transmit(u16 data); {…} UARTSend dataByte Byte Once the UART sent the Data, The TX interrupt will insert and the CPU will call ISR(USART_TXC_vect) { …….. }
  • 100.
    100 void (*Ptr_To_Trans_Int) (void); externvoid USART_callback_Trans_Int(void (*Ptr_to_Func)(void)) { Ptr_To_Trans_Int = Ptr_to_Func; } USART_Init (){…} ISR(USART_TXC_vect) { …….. } ISR(USART_TXC_vect) { (*Ptr_To_Trans_Int)(); } UARTSend dataByte Byte
  • 101.
    Pointers Tricks 101 How toRead C complex pointer Pointers on Embedded C Modularity Pointer with Constant
  • 102.
    Variable Quantifiers -const  const is used with a datatype declaration or definition to specify an unchanging value  const objects may not be changed 102
  • 103.
    Variable Quantifiers -const  const is used with a datatype declaration or definition to specify an unchanging value  const objects may not be changed 103
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    Complete the tableyes/no … 106
  • 107.
    107 int* ptr =&a; int* const ptr = &a; int const *ptr = &a; const int *ptr = &a;
  • 108.
    Complete the tableyes/no … 108 Try Now
  • 109.
    Complete the tableyes/no … 109
  • 110.
  • 111.
    References 111  CThe Complete Reference 4th Ed Herbert Schildt  A Tutorial on Data Representation  std::printf, std::fprintf, std::sprintf, std::snprintf…..  C Programming for Engineers, Dr. Mohamed Sobh  C programming expert.  fresh2refresh.com/c-programming  C programming Interview questions and answers  C – Preprocessor directives  Constant Pointers and Pointers to Constant A Subtle Difference in C Programming