strlen, strnlen_s
From cppreference.com
|
Defined in header
<string.h>
|
||
|
size_t
strlen
(
const
char
*
str
)
;
|
(1) | |
| (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
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_sis 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
Run this code
#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
References
- C23 standard (ISO/IEC 9899:2024):
-
- 7.24.6.3 The strlen function (p: TBD)
-
- K.3.7.4.4 The strnlen_s function (p: TBD)
- C17 standard (ISO/IEC 9899:2018):
-
- 7.24.6.3 The strlen function (p: TBD)
-
- K.3.7.4.4 The strnlen_s function (p: TBD)
- 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
|
|