strlen, strnlen_s

Header: <string.h>

  1. Returns the length of the given null-terminated byte string, that is, the number of characters in a character array whose first element is pointed to by str up to and not including the first null character.

# Declarations

size_t strlen( const char* str );

size_t strnlen_s( const char* str, size_t strsz );

(since C11)

# Parameters

# Notes

strnlen_s and wcsnlen_s are the only bounds-checked functions that do not invoke the runtime constraints handler. They are pure utility functions used to provide limited support for non-null terminated strings.

# Example

#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
#include <string.h>
 
int main(void)
{
    const char str[] = "How many characters does this string contain?";
 
    printf("without null character: %zu\n", strlen(str));
    printf("with null character:    %zu\n", sizeof str);
 
#ifdef __STDC_LIB_EXT1__
    printf("without null character: %zu\n", strnlen_s(str, sizeof str));
#endif
}

# See also