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Difference between revisions of "c/string/byte/strstr"

From cppreference.com
< c‎ | string‎ | byte
(→‎Example: const correctness)
m (→‎Example: make the substring bounds clearer with [])
 
(One intermediate revision by one user not shown)
Line 4: Line 4:
 
{{dcl header|string.h}}
 
{{dcl header|string.h}}
 
{{dcl|num=1|
 
{{dcl|num=1|
−
char *strstr( const char *str, const char *substr );
+
char* strstr( const char* str, const char* substr );
 
}}
 
}}
 
{{dcl|num=2|since=c23|
 
{{dcl|num=2|since=c23|
−
/*QChar*/ *strstr( /*QChar*/ *str, const char *substr );
+
/*QChar*/* strstr( /*QChar*/* str, const char* substr );
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
  
−
@1@Finds the first occurrence of the null-terminated byte string pointed to by {{tt|substr}} in the null-terminated byte string pointed to by {{tt|str}}. The terminating null characters are not compared.
+
@1@Finds the first occurrence of the null-terminated byte string pointed to by {{c|substr}} in the null-terminated byte string pointed to by {{c|str}}. The terminating null characters are not compared.
−
@2@ {{dsc_clang_type_generic_fun|char|str}}
+
@2@ {{dsc clang type generic fun|char|str}}
  
−
The behavior is undefined if either {{tt|str}} or {{tt|substr}} is not a pointer to a null-terminated byte string.
+
The behavior is undefined if either {{c|str}} or {{c|substr}} is not a pointer to a null-terminated byte string.
  
 
===Parameters===
 
===Parameters===
Line 23: Line 23:
  
 
===Return value===
 
===Return value===
−
Pointer to the first character of the found substring in {{tt|str}}, or a null pointer if such substring is not found. If {{tt|substr}} points to an empty string, {{tt|str}} is returned.
+
Pointer to the first character of the found substring in {{c|str}}, or a null pointer if such substring is not found. If {{c|substr}} points to an empty string, {{c|str}} is returned.
  
 
===Example===
 
===Example===
 
{{example
 
{{example
−
|
 
 
|code=
 
|code=
 
#include <stdio.h>
 
#include <stdio.h>
 
#include <string.h>
 
#include <string.h>
  
−
void find_str(char const *str, char const *substr)
+
void find_str(char const* str, char const* substr)
 
{
 
{
−
     char const *pos = strstr(str, substr);
+
     char const* pos = strstr(str, substr);
 
     if (pos)
 
     if (pos)
 
         printf(
 
         printf(
−
             "found the string '%s' in '%s' at position %td\n",
+
             "Found the string [%s] in [%s] at position %td\n",
 
             substr, str, pos - str
 
             substr, str, pos - str
 
         );
 
         );
 
     else
 
     else
 
         printf(
 
         printf(
−
             "the string '%s' was not found in '%s'\n",
+
             "The string [%s] was not found in [%s]\n",
 
             substr, str
 
             substr, str
 
         );
 
         );
Line 49: Line 48:
 
int main(void)
 
int main(void)
 
{
 
{
−
     char const *str = "one two three";
+
     char const* str = "one two three";
 
     find_str(str, "two");
 
     find_str(str, "two");
 
     find_str(str, "");
 
     find_str(str, "");
 
     find_str(str, "nine");
 
     find_str(str, "nine");
 
     find_str(str, "n");
 
     find_str(str, "n");
−
 
+
 
     return 0;
 
     return 0;
 
}
 
}
 
|output=
 
|output=
−
found the string 'two' in 'one two three' at position 4
+
Found the string [two] in [one two three] at position 4
−
found the string '' in 'one two three' at position 0
+
Found the string [] in [one two three] at position 0
−
the string 'nine' was not found in 'one two three'
+
The string [nine] was not found in [one two three]
−
found the string 'n' in 'one two three' at position 1
+
Found the string [n] in [one two three] at position 1
 
}}
 
}}
  
 
===References===
 
===References===
 +
{{ref std c23}}
 +
{{ref std|section=7.24.5.7|title=The strstr function|p=TBD}}
 +
{{ref std end}}
 
{{ref std c17}}
 
{{ref std c17}}
 
{{ref std|section=7.24.5.7|title=The strstr function|p=269}}
 
{{ref std|section=7.24.5.7|title=The strstr function|p=269}}

Latest revision as of 04:06, 5 October 2024

 
C
 
Strings library
 
Null-terminated byte strings
Functions
Character manipulation
Conversions to and from numeric formats
String manipulation
String examination
Memory manipulation
Miscellaneous
(C11)(C11)
 
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

Run this code
#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]
C++ documentation for strstr
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