# strstr

From cppreference.com
< c‎ | string‎ | byte

Defined in header `<string.h>` |  |
char *strstr( const char* str, const char* substr ); |  |

Finds the first occurrence of the null-terminated byte string pointed to by `substr` in the null-terminated byte string pointed to by `str`. The terminating null characters are not compared.

The behavior is undefined if either `str` or `substr` is not a pointer to a null-terminated byte string.

### Parameters

str | - | pointer to the null-terminated byte string to examine
substr | - | pointer to the null-terminated byte string to search for

### Return value

Pointer to the first character of the found substring in `str`, or NULL if no such substring is found. If `substr` points to an empty string, `str` is returned.

### Example

Run this code

    #include <string.h>
    #include <stdio.h>

    void find_str(char const* str, char const* substr)
    {
        char* pos = strstr(str, substr);
        if(pos) {
            printf("found the string '%s' in '%s' at position: %ld\n", substr, str, pos - str);
        } else {
            printf("the string '%s' was not found in '%s'\n", substr, str);
        }
    }

    int main(void)
    {
        char* str = "one two three";
        find_str(str, "two");
        find_str(str, "");
        find_str(str, "nine");
        find_str(str, "n");

        return 0;
    }

Output:

    found the string 'two' in 'one two three' at position: 4
    found the string '' in 'one two three' at position: 0
    the string 'nine' was not found in 'one two three'
    found the string 'n' in 'one two three' at position: 1

### References

- C11 standard (ISO/IEC 9899:2011):

  - 7.24.5.7 The strstr function (p: 369)

- C99 standard (ISO/IEC 9899:1999):

  - 7.21.5.7 The strstr function (p: 332)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.11.5.7 The strstr function

### See also

strchr | finds the first occurrence of a character (function)
strrchr | finds the last occurrence of a character (function)

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