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

From cppreference.com
< cpp‎ | string‎ | basic string
m (→‎Notes: plural (due to overloads))
m ({{c}}, capitalized 1st letter, fmt)
 
Line 18: Line 18:
 
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|ch}}.
+
@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 46: Line 46:
 
#include <type_traits>
 
#include <type_traits>
  
−
template <typename SubstrType>
+
template<typename SubstrType>
 
void test_substring(const std::string& str, SubstrType subs)
 
void test_substring(const std::string& str, SubstrType subs)
 
{
 
{

Latest revision as of 00:24, 1 June 2023

 
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basic_string::contains
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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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