strcspn

Returns the length of the maximum initial segment of the null-terminated byte string pointed to by dest, that consists of only the characters not found in the null-terminated byte string pointed to by src.

The behavior is undefined if either dest or src is not a pointer to a null-terminated byte string.

Parameters

Return value

The length of the maximum initial segment that contains only characters not found in the null-terminated byte string pointed to by src

Notes

The function name stands for "complementary span" because the function searches for characters not found in src, that is the complement of src.

Example

#include <string.h>
#include <stdio.h>
 
int main(void)
{
    const char *string = "abcde312$#@";
    const char *invalid = "*$#";
 
    size_t valid_len = strcspn(string, invalid);
    if(valid_len != strlen(string))
       printf("'%s' contains invalid chars starting at position %zu\n",
               string, valid_len);
}

'abcde312$#@' contains invalid chars starting at position 8

References