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strlen(3) Library Functions Manual strlen(3)

NAME

strlen - string length

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

#include <string.h>
size_t strlen(const char *s);

DESCRIPTION

The strlen() function calculates the length of the string pointed to by s, excluding the terminating null byte ('\0').

It is equivalent to


strnul(s) - s

RETURN VALUE

The strlen() function returns the number of bytes in the string pointed to by s.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
strlen () Thread safety MT-Safe

STANDARDS

C11, POSIX.1-2008.

HISTORY

POSIX.1-2001, C89, SVr4, 4.3BSD.

SEE ALSO

string(3), strnul(3), wcslen(3)

2026-08-10 Linux man-pages (unreleased)