strlen, strnlen_s
From cppreference.com
C
Concurrency support (C11)
Null-terminated byte strings
Functions
Character manipulation
Conversions to and from numeric formats
(C99)(C99)
(C99)(C99)
(C23)(C23)(C23)
String manipulation
String examination
Memory manipulation
Miscellaneous
(C11)(C11)
Defined in header
<string.h>
size_t strlen( const char* str );
(1)
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>.
[edit] Parameters
str
-
pointer to the null-terminated byte string to be examined
strsz
-
maximum number of characters to examine
[edit] 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.
[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
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
[edit] 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
[edit] See also
C++ documentation for strlen