strlen man page

strlen ā€” calculate the length of a string


#include <string.h>

size_t strlen(const char *s);


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

Return Value

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


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

Interface Attribute Value
strlen() Thread safety MT-Safe

Conforming to

POSIX.1-2001, POSIX.1-2008, C89, C99, C11, SVr4, 4.3BSD.

See Also

string(3), strnlen(3), wcslen(3), wcsnlen(3)


This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

lber-types(3), signal-safety(7), strchr(3), str_copy(3), str_diff(3), str_diffn(3), str_equal(3), string(3), str_len(3), strnlen(3), waffle_error(3), wcslen(3).

2016-03-15 GNU Linux Programmer's Manual