---
name: "strcasestr"
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/strcasestr"
---

# strcasestr(3)

string case-insensitive search substring

## NAME

strcasestr - string case-insensitive search substring

## LIBRARY

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

## SYNOPSIS

```
#define _GNU_SOURCE  // See feature_test_macros(7)
#include <string.h>
```

**char \*strcasestr(const char \****haystack***, const char \****needle***);**

## DESCRIPTION

**strcasestr**() is like **strstr**(), but ignores the case of both arguments.

## RETURN VALUE

See [**strstr**(3)](/strstr/3.md).

## ATTRIBUTES

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

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

## STANDARDS

GNU.

## HISTORY

GNU.

## SEE ALSO

[**string**(3)](/string/3.md), [**strstr**(3)](/strstr/3.md)