strlen, strnlen_s - cppreference.com (original) (raw)

Defined in header <string.h>
size_t strlen( const char* str );	(1)
size_t strnlen_s( const char* str, size_t strsz );	(2)	(since C11)

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.

The behavior is undefined if str is not a pointer to a null-terminated byte string.

Same as (1), except that the function returns zero if str is a null pointer and returns strsz if the null character was not found in the first strsz bytes of str.

The behavior is undefined if str is not a pointer to a null-terminated byte string and strsz is greater than the size of that character array.

As with all bounds-checked functions, strnlen_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 <string.h>.

[edit] Parameters

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

[edit] Return value

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

[edit] 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.

[edit] 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 }

Possible output:

without null character: 45 with null character: 46 without null character: 45

[edit] References