Null-terminated byte strings| Functions |
| Character manipulation |
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| Conversions to and from numeric formats |
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| String manipulation |
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| String examination |
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| Memory manipulation |
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| Miscellaneous |
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size_t strlen(constchar* str); | (1) | |
| (2) | (since C11) |
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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 bystr up to and not including the first null character.
The behavior is undefined ifstr is not a pointer to a null-terminated byte string.
2) Same as(1), except that the function returns zero ifstr is a null pointer and returnsstrsz if the null character was not found in the firststrsz bytes ofstr.
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 constant1 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 stringstr.
2) The length of the null-terminated byte stringstr on success, zero ifstr is a null pointer,strsz if the null character was not found.
strnlen_s andwcsnlen_s are the onlybounds-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){constchar 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: 45with null character: 46without 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
| returns the length of a wide string
(function)[edit] |
| returns the number of bytes in the next multibyte character
(function)[edit] |
|
