strstr

 

C

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Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Atomic operations (C11)

Thread support (C11)

Technical Specifications

 

Strings library

Byte strings

Multibyte strings

Wide strings

 

Null-terminated byte strings

Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to numeric formats
atof atoiatolatoll (C99) strtolstrtoll (C99)	strtoulstrtoull (C99) strtofstrtodstrtold (C99)(C99) strtoimaxstrtoumax (C99)(C99)
String manipulation
strcpystrcpy_s (C11)
strncpystrncpy_s (C11)
strcatstrcat_s (C11)
strncatstrncat_s (C11)
strxfrm
strdup (since C2x)
strndup (since C2x)
String examination
strlenstrnlen_s (C11) strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtokstrtok_s (C11)
Memory manipulation
memchr
memcmp
memsetmemset_s (C11)
memcpymemcpy_s (C11)
memmovememmove_s (C11)
memccpy (since C2x)
Miscellaneous
strerrorstrerror_sstrerrorlen_s (C11)(C11)

 

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 a null pointer if such substring is not 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)
C++ documentation for strstr