strstr

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.

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

#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;
}

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

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

strchr	finds the first occurrence of a character (function)
strrchr	finds the last occurrence of a character (function)
C++ documentation for `strstr`

Docs

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strstr

Parameters

Return value

Example

References

See also