NAME

strlen, strnlen — get length of fixed size string

SYNOPSIS

#include <string.h>

size_t strlen(const char *s);


[CX] size_t strnlen(const char *s, size_t maxlen);

DESCRIPTION

For strlen(): ^[CX]  The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2024 defers to the ISO C standard.

The strlen() function shall compute the number of bytes in the string to which s points, not including the terminating NUL character.

^[CX] The strnlen() function shall compute the smaller of the number of bytes in the array to which s points, not including any terminating NUL character, or the value of the maxlen argument. The strnlen() function shall never examine more than maxlen bytes of the array pointed to by s.

^[CX] The strlen() and strnlen() functions shall not change the setting of errno on valid input.

RETURN VALUE

The strlen() function shall return the length of s; no return value shall be reserved to indicate an error.

^[CX] The strnlen() function shall return the number of bytes preceding the first null byte in the array to which s points, if s contains a null byte within the first maxlen bytes; otherwise, it shall return maxlen.

ERRORS

No errors are defined.

EXAMPLES

Getting String Lengths

The following example sets the maximum length of key and data by using strlen() to get the lengths of those strings.

#include <string.h>
...
struct element {
    char *key;
    char *data;
};
...
char *key, *data;
int len;


*keylength = *datalength = 0;
...
if ((len = strlen(key)) > *keylength)
    *keylength = len;
if ((len = strlen(data)) > *datalength)
    *datalength = len;
...

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

strlcat, wcslen

XBD <string.h>

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

The RETURN VALUE section is updated to indicate that strlen() returns the length of s, and not s itself as was previously stated.

Issue 7

The strnlen() function is added from The Open Group Technical Standard, 2006, Extended API Set Part 1.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0344 [560] is applied.

Issue 8

Austin Group Defect 448 is applied, adding a requirement that strlen() and strnlen() do not change the setting of errno on valid input.

Austin Group Defect 986 is applied, adding strlcat() to the SEE ALSO section.