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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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STRLEN(3P) POSIX Programmer's Manual STRLEN(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
strlen, strnlen — get length of fixed size string
#include <string.h>
size_t strlen(const char *s);
size_t strnlen(const char *s, size_t maxlen);
For strlen(): 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.1‐2017 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.
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.
The strlen() function shall return the length of s; no return
value shall be reserved to indicate an error.
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.
No errors are defined.
The following sections are informative.
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;
...
None.
None.
None.
wcslen(3p)
The Base Definitions volume of POSIX.1‐2017, string.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 STRLEN(3P)
Pages that refer to this page: string.h(0p), localeconv(3p), strnlen(3p), wcslen(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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