String.indexOf function in C

Question

Is there a C library function that will return the index of a character in a string?

So far, all I've found are functions like strstr that will return the found char *, not it's location in the original string.

Answer 1

If you are not totally tied to pure C and can use string.h there is strchr() See here

Answer 2

strstr returns a pointer to the found character, so you could use pointer arithmetic: (Note: this code not tested for its ability to compile, it's one step away from pseudocode.)

char * source = "test string";         /* assume source address is */
                                       /* 0x10 for example */
char * found = strstr( source, "in" ); /* should return 0x18 */
if (found != NULL)                     /* strstr returns NULL if item not found */
{
  int index = found - source;          /* index is 8 */
                                       /* source[8] gets you "i" */
}

Answer 3

EDIT: strchr is better only for one char. Pointer aritmetics says "Hellow!":

char *pos = strchr (myString, '#');
int pos = pos ? pos - myString : -1;

Important: strchr () returns NULL if no string is found

Answer 4

You can use strstr to accomplish what you want. Example:

char *a = "Hello World!";
char *b = strstr(a, "World");

int position = b - a;

printf("the offset is %i\n", position);

This produces the result:

the offset is 6

Answer 5

I think that

size_t strcspn ( const char * str1, const char * str2 );

is what you want. Here is an example pulled from here:

/* strcspn example */
#include <stdio.h>
#include <string.h>

int main ()
{
  char str[] = "fcba73";
  char keys[] = "1234567890";
  int i;
  i = strcspn (str,keys);
  printf ("The first number in str is at position %d.\n",i+1);
  return 0;
}