Incompatibilities between C and C++

Here we will see some incompatibilities between C and C++. Some C codes that can be compiled using C compiler, but does not compile in C++ compiler. And also returns error.

• We can define function using a syntax, that optionally specify the argument types after the argument list.

Example

#include<stdio.h> void my_function(x, y)int x;int y; { // Not valid in C++    printf("x = %d, y = %d", x, y); } int main() {    my_function(10, 20); }

Output

x = 10, y = 20

Output

Error in C++ :- x and y was not declared in this scope

• In C, or some older version of C++, the default variable type is integer. But in newer C++, it will generate an error.

Example

#include<stdio.h> main() {    const x = 10;    const y = 20;    printf("x = %d, y = %d", x, y); }

Output

x = 10, y = 20

Output

Error in C++ :- x does not name a type y does not name a type

• In C, the global data objects may be declared many times without using the extern keyword. C compiler considers it once for multiple declarations.

Example

#include<stdio.h> int x; int x; int main() {    x = 10;    printf("x = %d", x); }

Output

x = 10

Output

Error in C++ :- Redefinition of int x

• In C, we can use void pointer as the right hand operator of an assignment to or initialize the variable of any pointer type.

Example

#include<stdio.h> #include<malloc.h> void my_function(int n) {    int* ptr = malloc(n* sizeof(int)); //implicitly convert void* to int*    printf("Array created. Size: %d", n); } main() {    my_function(10); }

Output

Array created. Size: 10

Output

Error in C++ :- Invalid conversion of void* to int*

• In C, if the argument type is not specified, we can pass multiple arguments.

Example

#include<stdio.h> void my_function() {    printf("Inside my_function"); } main() {    my_function(10, "Hello", 2.568, 'a'); }

Output

Inside my_function

Output

Error in C++ :- Too many arguments to function 'void my_function()'