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Difference between revisions of "cpp/string/basic string/contains"

From cppreference.com
< cpp‎ | string‎ | basic string
m (Reverted edits by 93.100.163.120 (talk) to last revision by Fruderica)
m ({{c}}, capitalized 1st letter, fmt)
 
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−
{{cpp/string/basic_string/title | contains}}
+
{{cpp/string/basic_string/title|contains}}
 
{{cpp/string/basic_string/navbar}}
 
{{cpp/string/basic_string/navbar}}
 
{{dcl begin}}
 
{{dcl begin}}
−
{{dcl | num=1 |since=c++23|1=
+
{{dcl|num=1|since=c++23|1=
−
constexpr bool contains( std::basic_string_view<CharT,Traits> sv )
+
constexpr bool
−
    const noexcept;
+
    contains( std::basic_string_view<CharT,Traits> sv ) const noexcept;
 
}}
 
}}
−
{{dcl | num=2 |since=c++23|1=
+
{{dcl|num=2|since=c++23|1=
−
constexpr bool contains( CharT c ) const noexcept;
+
constexpr bool
 +
    contains( CharT ch ) const noexcept;
 
}}
 
}}
−
{{dcl | num=3 |since=c++23|1=
+
{{dcl|num=3|since=c++23|1=
−
constexpr bool contains( const CharT* s ) const;
+
constexpr bool
 +
    contains( const CharT* s ) const;
 
}}
 
}}
 
{{dcl end}}
 
{{dcl end}}
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Checks if the string contains the given substring. The substring may be one of the following:
 
Checks if the string contains the given substring. The substring may be one of the following:
  
−
@1@ a string view {{tt|sv}} (which may be a result of implicit conversion from another {{tt|std::basic_string}}).
+
@1@ A string view {{c|sv}} (which may be a result of implicit conversion from another {{tt|std::basic_string}}).
−
@2@ a single character {{tt|c}}.
+
@2@ A single character {{c|ch}}.
−
@3@ a null-terminated character string {{tt|s}}.
+
@3@ A null-terminated character string {{c|s}}.
  
 
All three overloads are equivalent to {{c|1=return find(x) != npos;}}, where {{tt|x}} is the parameter.
 
All three overloads are equivalent to {{c|1=return find(x) != npos;}}, where {{tt|x}} is the parameter.
Line 24: Line 26:
 
===Parameters===
 
===Parameters===
 
{{par begin}}
 
{{par begin}}
−
{{par | sv | a string view which may be a result of implicit conversion from another {{tt|std::basic_string}}}}
+
{{par|sv|a string view which may be a result of implicit conversion from another {{tt|std::basic_string}}}}
−
{{par | c | a single character}}
+
{{par|ch|a single character}}
−
{{par | s | a null-terminated character string}}
+
{{par|s|a null-terminated character string}}
 
{{par end}}
 
{{par end}}
  
 
===Return value===
 
===Return value===
 
{{c|true}} if the string contains the provided substring, {{c|false}} otherwise.
 
{{c|true}} if the string contains the provided substring, {{c|false}} otherwise.
 +
 +
===Notes===
 +
{{feature test macro|__cpp_lib_string_contains|{{tt|contains}} functions|std=C++23|value=202011L}}
  
 
===Example===
 
===Example===
 
{{example
 
{{example
−
| code=
+
|code=
 +
#include <iomanip>
 
#include <iostream>
 
#include <iostream>
 +
#include <string>
 
#include <string_view>
 
#include <string_view>
−
#include <string>
+
#include <type_traits>
  
−
template <typename SubstrType>
+
template<typename SubstrType>
−
void test_substring_print(const std::string& str, SubstrType subs)
+
void test_substring(const std::string& str, SubstrType subs)
 
{
 
{
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     std::cout << '\'' << str << "' contains '" << subs << "': " <<
+
     constexpr char delim = std::is_scalar_v<SubstrType> ? '\'' : '\"';
−
        str.contains(subs) << '\n';
+
    std::cout << std::quoted(str)
 +
              << (str.contains(subs) ? " contains "
 +
                                    : " does not contain ")
 +
              << std::quoted(std::string{subs}, delim) << '\n';
 
}
 
}
  
 
int main()
 
int main()
 
{
 
{
−
     std::boolalpha(std::cout);   
+
     using namespace std::literals;
−
    auto helloWorld = std::string("hello world");
+
−
 
+
−
    test_substring_print(helloWorld, std::string_view("hello"));
+
−
 
+
−
    test_substring_print(helloWorld, std::string_view("goodbye"));
+
  
−
     test_substring_print(helloWorld, 'w');
+
     auto helloWorld = "hello world"s;
  
−
     test_substring_print(helloWorld, 'x');
+
     test_substring(helloWorld, "hello"sv);
 +
    test_substring(helloWorld, "goodbye"sv);
 +
    test_substring(helloWorld, 'w');
 +
    test_substring(helloWorld, 'x');
 
}
 
}
−
| output=
+
|output=
−
'hello world' contains 'hello': true
+
"hello world" contains "hello"
−
'hello world' contains 'goodbye': false
+
"hello world" does not contain "goodbye"
−
'hello world' contains 'w': true
+
"hello world" contains 'w'
−
'hello world' contains 'x': false
+
"hello world" does not contain 'x'
 
}}
 
}}
  
 
===See also===
 
===See also===
 
{{dsc begin}}
 
{{dsc begin}}
−
{{dsc inc | cpp/string/basic_string/dsc starts_with}}
+
{{dsc inc|cpp/string/basic_string/dsc starts_with}}
−
{{dsc inc | cpp/string/basic_string/dsc ends_with}}
+
{{dsc inc|cpp/string/basic_string/dsc ends_with}}
−
{{dsc inc | cpp/string/basic_string/dsc find}}
+
{{dsc inc|cpp/string/basic_string/dsc find}}
−
{{dsc inc | cpp/string/basic_string/dsc substr}}
+
{{dsc inc|cpp/string/basic_string/dsc substr}}
 +
{{dsc inc|cpp/string/basic_string_view/dsc {{SUBPAGENAMEE}}}}
 
{{dsc end}}
 
{{dsc end}}
  
 
{{langlinks|de|es|fr|it|ja|pl|pt|ru|zh}}
 
{{langlinks|de|es|fr|it|ja|pl|pt|ru|zh}}

Latest revision as of 00:24, 1 June 2023

 
C++
 
Strings library
 
std::basic_string
Member functions
(C++23)
Element access
(DR*)
(DR*)
(C++17)
Iterators
(C++11)
(C++11)
(C++11)
(C++11)
Capacity
(DR*)
Modifiers
(C++23)
(DR*)
(C++23)
(C++23)
(C++23)  
Search
Operations
(C++20)
(C++20)
basic_string::contains
(C++23)
Constants
Non-member functions
(C++20)(C++20)
I/O
Comparison
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Numeric conversions
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)(C++11)
(C++11)
(C++11)
Literals
(C++14)
Helper classes
(C++11)
Deduction guides (C++17)

 
constexpr bool
    contains( std::basic_string_view<CharT,Traits> sv ) const noexcept;
 (1) (since C++23)
constexpr bool
    contains( CharT ch ) const noexcept;
 (2) (since C++23)
constexpr bool
    contains( const CharT* s ) const;
 (3) (since C++23)

Checks if the string contains the given substring. The substring may be one of the following:

1) A string view sv (which may be a result of implicit conversion from another std::basic_string).
2) A single character ch.
3) A null-terminated character string s.

All three overloads are equivalent to return find(x) != npos;, where x is the parameter.

Contents

[edit] Parameters

sv - a string view which may be a result of implicit conversion from another std::basic_string
ch - a single character
s - a null-terminated character string

[edit] Return value

true if the string contains the provided substring, false otherwise.

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_string_contains 202011L (C++23) contains functions

[edit] Example

Run this code
#include <iomanip>
#include <iostream>
#include <string>
#include <string_view>
#include <type_traits>
 
template<typename SubstrType>
void test_substring(const std::string& str, SubstrType subs)
{
    constexpr char delim = std::is_scalar_v<SubstrType> ? '\'' : '\"';
    std::cout << std::quoted(str)
              << (str.contains(subs) ? " contains "
                                     : " does not contain ")
              << std::quoted(std::string{subs}, delim) << '\n';
}
 
int main()
{
    using namespace std::literals;
 
    auto helloWorld = "hello world"s;
 
    test_substring(helloWorld, "hello"sv);
    test_substring(helloWorld, "goodbye"sv);
    test_substring(helloWorld, 'w');
    test_substring(helloWorld, 'x');
}

Output: 

"hello world" contains "hello"
"hello world" does not contain "goodbye"
"hello world" contains 'w'
"hello world" does not contain 'x'

[edit] See also

(C++20)
 checks if the string starts with the given prefix
(public member function) [edit]
(C++20)
 checks if the string ends with the given suffix
(public member function) [edit]
finds the first occurrence of the given substring
(public member function) [edit]
returns a substring
(public member function) [edit]
(C++23)
 checks if the string view contains the given substring or character
(public member function of std::basic_string_view<CharT,Traits>) [edit]
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