wcslen, wcsnlen_s

Defined in header <wchar.h>
size_t wcslen( const wchar_t *str );
(1) (since C95)
size_t wcsnlen_s(const wchar_t *str, size_t strsz);
(2) (since C11)
1) Returns the length of a wide string, that is the number of non-null wide characters that precede the terminating null wide character.
2) Same as (1), except that the function returns zero if str is a null pointer and returns strsz if the null wide character was not found in the first strsz wide characters of src As with all bounds-checked functions, wcslen_s is only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdio.h>..


str - pointer to the null-terminated wide string to be examined
strsz - maximum number of wide characters to examine

Return value

1) The length of the null-terminated wide string str.
2) The length of the null-terminated wide string str on success, zero if str is a null pointer, strsz if the null wide character was not found.


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.


#include <wchar.h>
#include <stdio.h>
int main(void)
    wchar_t str[] = L"How many wide characters does this string contain?";
    printf("without null character: %zu\n", wcslen(str));
    printf("with null character: %zu\n", sizeof str / sizeof *str);


without null character: 50
with null character: 51


  • C11 standard (ISO/IEC 9899:2011):
    • The wcslen function (p: 439)
    • K. The wcsnlen_s function (p: 646-647)
  • C99 standard (ISO/IEC 9899:1999):
    • The wcslen function (p: 385)

See also

returns the length of a given string
C++ documentation for wcslen

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