In C how do I find the index of a character within a string?

Question

Suppose I have a string "qwerty" and I wish to find the index position of character e in it. How do I do it in C? (In this case the index would be 2)

I found strchr function but that returns a pointer to the character and not the index.

Please help me out!

Thanks, Boda Cydo.

Answer 1

Just subtract the string address from what strchr returns:

char *string = "qwerty";
char *e;
int index;

e = strchr(string, 'e');
index = (int)(e - string);

Answer 2

void myFunc(char* str, char c)
{
    char* ptr;
    int index;

    ptr = strchr(str, c);
    if (ptr == NULL)
    {
        printf("Character not found\n");
        return;
    }

    index = ptr - str;

    printf("The index is %d\n", index);
    ASSERT(str[index] == c);  // Verify that the character at index is the one we want.
}

This code is currently untested, but it demonstrates the proper concept.

Answer 3

You can also use strcspn(string, "e") but this may be much slower since it's able to handle searching for multiple possible characters. Using strchr and subtracting the pointer is the best way.