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strstr

From cppreference.com
< c‎ | string‎ | byte
Defined in header <string.h>
char* strstr( const char* str, const char* substr );
(1)
/*QChar*/* strstr( /*QChar*/* str, const char* substr );
(2) (since C23)
1) 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.
2) Type-generic function equivalent to (1). Let T be an unqualified character object type.
  • If str is of type const T*, the return type is const char*.
  • Otherwise, if str is of type T*, the return type is char*.
  • Otherwise, the behavior is undefined.
If a macro definition of each of these generic functions is suppressed to access an actual function (e.g. if (strstr) or a function pointer is used), the actual function declaration (1) becomes visible.

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

Contents

[edit] Parameters

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

[edit] 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.

[edit] Example

#include <stdio.h>
#include <string.h>
 
void find_str(char const* str, char const* substr)
{
    char const* pos = strstr(str, substr);
    if (pos)
        printf(
            "Found the string [%s] in [%s] at position %td\n",
            substr, str, pos - str
        );
    else
        printf(
            "The string [%s] was not found in [%s]\n",
            substr, str
        );
}
 
int main(void)
{
    char const* 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

[edit] References

  • C23 standard (ISO/IEC 9899:2024):
  • 7.24.5.7 The strstr function (p: TBD)
  • 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

[edit] See also

finds the first occurrence of a character
(function) [edit]
finds the last occurrence of a character
(function) [edit]