strcspn

Header: <string.h>

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.

# Declarations

size_t strcspn( const char *dest, const char *src );

# Parameters

dest: pointer to the null-terminated byte string to be analyzed
src: pointer to the null-terminated byte string that contains the characters to search for

# 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);
}