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Difference between revisions of "cpp/string/basic string view/starts with"

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===Notes===
 
===Notes===
−
{{feature test macro|__cpp_lib_starts_ends_with|String prefix and suffix checking ({{lc|starts_with()}} and {{lc|ends_with()}}|std=C++20|value=201711L}}
+
{{feature test macro|__cpp_lib_starts_ends_with|String prefix and suffix checking: {{lc|starts_with()}} and {{lc|ends_with()}}|std=C++20|value=201711L}}
  
 
===Example===
 
===Example===

Revision as of 09:49, 14 November 2022

 
C++
 
Strings library
 
std::basic_string_view
 
constexpr bool starts_with( basic_string_view sv ) const noexcept;
 (1) (since C++20)
constexpr bool starts_with( CharT ch ) const noexcept;
 (2) (since C++20)
constexpr bool starts_with( const CharT* s ) const;
 (3) (since C++20)

Checks if the string view begins with the given prefix, where

1) the prefix is a string view. Effectively returns substr(0, sv.size()) == sv
2) the prefix is a single character. Effectively returns !empty() && Traits::eq(front(), ch)
3) the prefix is a null-terminated character string. Effectively returns starts_with(basic_string_view(s))

Contents

Parameters

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

Return value

true if the string view begins with the provided prefix, false otherwise.

Notes

Feature-test macro Value Std Feature
__cpp_lib_starts_ends_with 201711L (C++20) String prefix and suffix checking: starts_with() and ends_with()

Example

Run this code
#include <iostream>
#include <string_view>
 
int main()
{
    using namespace std::literals;
 
    std::cout
        << std::boolalpha
 
        // bool starts_with(basic_string_view x) const noexcept;
        << "https://cppreference.com"sv.starts_with("http"sv) << ' ' // true
        << "https://cppreference.com"sv.starts_with("ftp"sv) << ' '  // false
 
        // bool starts_with(CharT x) const noexcept;
        << "C++20"sv.starts_with('C') << ' ' // true
        << "C++20"sv.starts_with('J') << ' ' // false
 
        // bool starts_with(const CharT* x) const;
        << std::string_view("string_view").starts_with("string") << ' ' // true
        << std::string_view("string_view").starts_with("String") << ' ' // false
        << '\n';
}

Output: 

true false true false true false

See also

(C++20)
 checks if the string view ends with the given suffix
(public member function) [edit]
(C++20)
 checks if the string starts with the given prefix
(public member function of std::basic_string<CharT,Traits,Allocator>) [edit]
(C++20)
 checks if the string ends with the given suffix
(public member function of std::basic_string<CharT,Traits,Allocator>) [edit]
(C++23)
 checks if the string contains the given substring or character
(public member function of std::basic_string<CharT,Traits,Allocator>) [edit]
(C++23)
 checks if the string view contains the given substring or character
(public member function) [edit]
compares two views
(public member function) [edit]
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