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std::basic_string_view<CharT,Traits>::starts_with

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)).

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 Comment
__cpp_lib_starts_ends_with 201711L (C++20) String prefix and suffix checking: starts_with() and ends_with()

Example

#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") << '\n'; // false
}

Output:

true false true false true false

See also

(C++20)
 checks if the string view ends with the given suffix
(public member function)
(C++20)
 checks if the string starts with the given prefix
(public member function of std::basic_string<CharT,Traits,Allocator>)
(C++20)
 checks if the string ends with the given suffix
(public member function of std::basic_string<CharT,Traits,Allocator>)
(C++23)
 checks if the string contains the given substring or character
(public member function of std::basic_string<CharT,Traits,Allocator>)
(C++23)
 checks if the string view contains the given substring or character
(public member function)
(C++17)
 compares two views
(public member function)

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