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'\" t
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH strlen 3 2025-05-17 "Linux man-pages (unreleased)"
.SH NAME
strlen \- calculate the length of a string
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <string.h>
.P
.BI "size_t strlen(const char *" s );
.fi
.SH DESCRIPTION
The
.BR strlen ()
function calculates the length of the string pointed to by
.IR s ,
excluding the terminating null byte (\[aq]\[rs]0\[aq]).
.SH RETURN VALUE
The
.BR strlen ()
function returns the number of bytes in the string pointed to by
.IR s .
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR strlen ()
T} Thread safety MT-Safe
.TE
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
POSIX.1-2001, C89, SVr4, 4.3BSD.
.SH NOTES
In cases where the input buffer may not contain
a terminating null byte,
.BR strnlen (3)
should be used instead.
.SH SEE ALSO
.BR string (3),
.BR strnlen (3),
.BR wcslen (3),
.BR wcsnlen (3)
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