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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string_view

Member functions basic_string_view::basic_string_view    basic_string_view::operator= Iterators basic_string_view::beginbasic_string_view::cbegin basic_string_view::endbasic_string_view::cend basic_string_view::rbeginbasic_string_view::crbegin basic_string_view::rendbasic_string_view::crend Element access basic_string_view::at basic_string_view::operator[] basic_string_view::front basic_string_view::back basic_string_view::data Capacity basic_string_view::sizebasic_string_view::length basic_string_view::max_size basic_string_view::empty Modifiers basic_string_view::remove_prefix basic_string_view::remove_suffix basic_string_view::swap

Operations basic_string_view::copy basic_string_view::substr basic_string_view::compare basic_string_view::starts_with (C++20) basic_string_view::ends_with (C++20) basic_string_view::contains (C++23) basic_string_view::find basic_string_view::rfind basic_string_view::find_first_of basic_string_view::find_last_of basic_string_view::find_first_not_of basic_string_view::find_last_not_of Constants basic_string_view::npos Non-member functions operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) operator<< operator""sv Helper classes hash<std::string_view>hash<std::wstring_view>hash<std::u8string_view>hash<std::u16string_view>hash<std::u32string_view> (C++20) Deduction guides(C++20)

 

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	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

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