strstr

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

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

#include <string.h>
#include <stdio.h>
 
void find_str(char const* str, char const* substr) 
{
    char* pos = strstr(str, substr);
    pos ? printf("found the string '%s' in '%s' at position %td\n", 
                 substr, str, pos - str)
        : 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;
}

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

• C17 standard (ISO/IEC 9899:2018):
• 7.24.5.7 The strstr function (p: 269)
• 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