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