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

From cppreference.com
m (→‎Example: -<iostream>)
m (→‎Example: comments: rm insignificant (for this example) parts of function signatures)
Line 43: Line 43:
 
     assert
 
     assert
 
     (""
 
     (""
−
         // (1) starts_with(basic_string_view x) const noexcept;
+
         // (1) starts_with( basic_string_view )
 
         && "https://cppreference.com"sv.starts_with("http"sv) == true
 
         && "https://cppreference.com"sv.starts_with("http"sv) == true
 
         && "https://cppreference.com"sv.starts_with("ftp"sv) == false
 
         && "https://cppreference.com"sv.starts_with("ftp"sv) == false
 
   
 
   
−
         // (2) starts_with(CharT x) const noexcept;
+
         // (2) starts_with( CharT )
 
         && "C++20"sv.starts_with('C') == true
 
         && "C++20"sv.starts_with('C') == true
 
         && "C++20"sv.starts_with('J') == false
 
         && "C++20"sv.starts_with('J') == false
 
   
 
   
−
         // (3) starts_with(const CharT* x) const;
+
         // (3) starts_with( const CharT* )
 
         && std::string_view("string_view").starts_with("string") == true
 
         && std::string_view("string_view").starts_with("string") == true
 
         && std::string_view("string_view").starts_with("String") == false
 
         && std::string_view("string_view").starts_with("String") == false

Revision as of 07:23, 17 August 2023

 
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 <cassert>
#include <string_view>
 
int main()
{
    using namespace std::literals;
 
    assert
    (""
        // (1) starts_with( basic_string_view )
        && "https://cppreference.com"sv.starts_with("http"sv) == true
        && "https://cppreference.com"sv.starts_with("ftp"sv) == false
 
        // (2) starts_with( CharT )
        && "C++20"sv.starts_with('C') == true
        && "C++20"sv.starts_with('J') == false
 
        // (3) starts_with( const CharT* )
        && std::string_view("string_view").starts_with("string") == true
        && std::string_view("string_view").starts_with("String") == 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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