---
name: "strstr"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/strstr"
---

# strstr(3)

locate a substring in a string

## NAME

**strstr**, **strcasestr**, **strnstr** – locate a substring in a string

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<string.h\>**

*char* *\**\

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

*char* *\**\

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

*char* *\**\

**strnstr**(*const char \*haystack*, *const char \*needle*, *size\_t len*);

**#include \<string.h\>**

**#include \<xlocale.h\>**

*char* *\**\

**strcasestr\_l**(*const char \*haystack*, *const char \*needle*, *locale\_t loc*);

## DESCRIPTION

The **strstr**() function locates the first occurrence of the null-terminated string *needle* in the null-terminated string *haystack*.

The **strcasestr**() function is similar to **strstr**(), but ignores the case of both strings.

The **strnstr**() function locates the first occurrence of the null-terminated string *needle* in the string *haystack*, where not more than *len* characters are searched. Characters that appear after a ‘\\0’ character are not searched. Since the **strnstr**() function is a FreeBSD specific API, it should only be used when portability is not a concern.

While the **strcasestr**() function uses the current locale, the **strcasestr\_l**() function may be passed a locale directly. See [xlocale(3)](/xlocale/3.md) for more information.

## RETURN VALUES

If *needle* is an empty string, *haystack* is returned; if *needle* occurs nowhere in *haystack*, NULL is returned; otherwise a pointer to the first character of the first occurrence of *needle* is returned.

## EXAMPLES

The following sets the pointer *ptr* to the "Bar Baz" portion of *largestring*:

```
const char *largestring = "Foo Bar Baz";
const char *smallstring = "Bar";
char *ptr;
ptr = strstr(largestring, smallstring);
```

The following sets the pointer *ptr* to NULL, because only the first 4 characters of *largestring* are searched:

```
const char *largestring = "Foo Bar Baz";
const char *smallstring = "Bar";
char *ptr;
ptr = strnstr(largestring, smallstring, 4);
```

## SEE ALSO

[memchr(3)](/memchr/3.md), [memmem(3)](/memmem/3.md), [strchr(3)](/strchr/3.md), [strcspn(3)](/strcspn/3.md), [strpbrk(3)](/strpbrk/3.md), [strrchr(3)](/strrchr/3.md), [strsep(3)](/strsep/3.md), [strspn(3)](/strspn/3.md), [strtok(3)](/strtok/3.md), [wcsstr(3)](/wcsstr/3.md), [xlocale(3)](/xlocale/3.md)

## STANDARDS

The **strstr**() function conforms to ISO/IEC 9899:1990 (“ISO C90”).