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) |
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. The behavior is undefined if
str
is not a pointer to a null-terminated byte string. 2) 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 both
str
points to a character array which lacks the null character and the size of that character array < strsz
; in other words, an erroneous value of strsz
does not expose the impending buffer overflow. 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
. Parameters
str | - | pointer to the null-terminated byte string to be examined |
strsz | - | maximum number of characters to examine |
Return value
1) The length of the null-terminated byte string
str
. 2) 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.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 <string.h> #include <stdio.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 }
Output:
without null character: 45 with null character: 46 without null character: 45
References
- C11 standard (ISO/IEC 9899:2011):
- 7.24.6.3 The strlen function (p: 372)
- K.3.7.4.4 The strnlen_s function (p: 623)
- C99 standard (ISO/IEC 9899:1999):
- 7.21.6.3 The strlen function (p: 334)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.11.6.3 The strlen function
See also
(C95)(C11) | returns the length of a wide string (function) |
returns the number of bytes in the next multibyte character (function) | |
C++ documentation for strlen |
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