Implementation of c string functions

Implementation of c string functions

• 1.
  Prepared by Mohammed Sikander TechnicalLead Cranes Software International Limited
• 2.
   size_t strlen(constchar *str); mohammed.sikander@cranessoftware.com 2 size_t mystrlen(const char *str) { const char *end = str; while( *end != ‘0’) end++; return end – str; }
• 3.
  char * strcpy(char*dest, const char *src); mohammed.sikander@cranessoftware.com 3 void mystrcpy(char *dest, const char *src) { while(1) { *dest = *src; if(*dest == ‘0’) return; src++; dest++; } }
• 4.
  char * strcpy(char*dest, const char *src); mohammed.sikander@cranessoftware.com 4 void mystrcpy(char *dest, const char *src) { while((*dest++ = *src++)) { } }
• 5.
  mohammed.sikander@cranessoftware.com 5 void mystrncpy(char*dest, const char *src, size_t n) { for(int i = 0 ; i < n ; i++) { *dest = *src; if(*dest == ‘0’) return; src++; dest++; } } int main( ) { char str[20] = “KARNATAKA”; char s1[20] = “ABCDEFGHIJKLMN”; char s2[20] = “ABCDEFGHIJKLMN”; mystrncpy(s1 , str ,5); mystrncpy(s2 , str , 12); printf(“s1 = %s n” , s1); printf(“s2 = %s n” , s2); }
• 6.
  int strcmp(const char*str1 , const char *str2); mohammed.sikander@cranessoftware.com 6 int mystrcmp(const char *str1 , const char *str2) { while(1) { if(*str1 != *str2) return *str1 - *str2; if(*str1 == ‘0’) return 0; str1++; str2++; } } while(*str1 == *str2 && *str1 != ‘0’) { str1++; str2++; } return *str1 - *str2;
• 7.
  int strncmp(const char*str1 , const char *str2,size_t n); mohammed.sikander@cranessoftware.com 7 int mystrcmp(const char *str1 , const char *str2,size_t n) { for(int I = 0 ; i < n ; i++) { if(*str1 != *str2) return *str1 - *str2; if(*str1 == ‘0’) return 0; str1++; str2++; } return 0; } int main( ) { char str1[ ] = “ BANGALORE”; char str2[ ] = “BANGKOK”; int res; res = mystrncmp(str1 , str2 , 3) ; printf(“res = %d “ , res); res = mystrncmp(str1 , str2 , 5) ; printf(“res = %d “ , res); }
• 8.
  int strcmpi(const char*str1 , const char *str2); mohammed.sikander@cranessoftware.com 8 int mystrcmpi(const char *str1 , const char *str2) { while(1) { char x = toupper(*str1); char y = toupper(*str2); if(x != y) return x - y; if(*str1 == ‘0’) return 0; str1++; str2++; } } int main( ) { char str1 [ ] = “ BANGALORE “; char str2 [ ] = “bangalore”; int res; res = mystrcmpi( str1 , str2); printf(“res = %d “ , res); }
• 9.
  void mystrrev(char *startptr) { intlen = strlen(startptr); char *endptr = startptr + len - 1; while(startptr < endptr) { myswap(startptr , endptr); startptr++; endptr--; } } mohammed.sikander@cranessoftware.com 9 void myswap(char *a,char *b) { char temp = *a; *a = *b; *b = temp; } int main( ) { char str[ ] = “ SIKANDER”; printf(“str = %s” , str); mystrrev(str); printf(“n After Reverse n”); printf(“str = %s” , str); }
• 10.
  char *strchr(const char*str, char key); char *mystrchr(const char *str , char key) { while(*str != ‘0’) { if(*str == key) return str; str++; } return NULL; } mohammed.sikander@cranessoftware.com 10 int main( ) { char str[ ] = “BANGALORE”; char *ptr; ptr = mystrchr(str , ‘A’); if(ptr == NULL) printf(“Key Not found”); else printf(“Found at index “ , ptr – str); ptr = mystrchr(str , ‘C’); if(ptr == NULL) printf(“Key Not found”); else printf(“Found at index “ , ptr – str); }
• 11.
  char *strrchr(const char*str, char key); char *mystrrchr(const char *start , char key) { int len = strlen(str); char *end = start + len – 1; while(end > start) { if(*end == key) return end; end--; } return NULL; } mohammed.sikander@cranessoftware.com 11 int main( ) { char str[ ] = “BANGALORE”; char *ptr; ptr = mystrrchr(str , ‘A’); if(ptr == NULL) printf(“Key Not found”); else printf(“Found at index “ , ptr – str); ptr = mystrrchr(str , ‘C’); if(ptr == NULL) printf(“Key Not found”); else printf(“Found at index “ , ptr – str); }
• 12.
  char * mystrcat(char*dest , const char *src) { int len = strlen(dest); mystrcpy(dest + len , src); return dest; } mohammed.sikander@cranessoftware.com 12 char *mystrncat(char *dest , const char *src,size_t n) { int len = strlen(dest); mystrncpy(dest + len , src , n ); }
• 13.
  char * mystrstr(char*str , char *key) { int len = strlen(key); char *ptr; while(1) { ptr = strchr(str , *key); if(ptr == NULL) return NULL; int res = strncmp(ptr , key , len); if(res != 0) return ptr; str = ptr + 1; } } mohammed.sikander@cranessoftware.com 13 Main String : BANGALORE Sub String to Search : GAL GALA LOT