---
name: "strnlen"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/strnlen"
---

# strnlen(3)

nonstring length

## NAME

strnlen - nonstring length

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <string.h>  // see memory.h(3head)
```

**size\_t strnlen(const char** strn**\[\], size\_t** n**);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**strnlen**():

```
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _GNU_SOURCE
```

## DESCRIPTION

This function determines the length of the character sequence contained in the array pointed to by *strn*.

If *strn* contains a string, the array can have less than *n* elements.

It is equivalent to

```
(memchr(strn, '\0', n) ?: strn + n) - strn
```

## RETURN VALUE

The **strnlen**() function returns the number of nonnull characters in *strn*.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **strnlen**() | Thread safety | MT-Safe |

## STANDARDS

POSIX.1-2008.

## HISTORY

POSIX.1-2008.

## SEE ALSO

[**memory.h**(3head)](/memory.h/3head.md)