std::basic_string<CharT,Traits,Allocator>:: starts_with

From cppreference.com
C++
Strings library
std::basic_string
Member functions
(C++23)
Element access
( DR* )
( DR* )
(C++17)
Iterators
(C++11)
(C++11)
(C++11)
(C++11)
Capacity
( DR* )
Modifiers
(C++23)
( DR* )
(C++23)
(C++23)
(C++23)
Search
Operations
basic_string::starts_with
(C++20)
(C++20)
(C++23)
Constants
Non-member functions
(C++20) (C++20)
I/O
Comparison
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20) (C++20)
Numeric conversions
(C++11) (C++11) (C++11)
(C++11) (C++11)
(C++11) (C++11) (C++11)
(C++11)
(C++11)
Literals
(C++14)
Helper classes
(C++11)
Deduction guides (C++17)

constexpr bool
starts_with ( std:: basic_string_view < CharT,Traits > 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 begins with the given prefix. The prefix 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 effectively return std:: basic_string_view < CharT, Traits > ( data ( ) , size ( ) ) . starts_with ( x ) , where x is the parameter.

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

Return value

true if the string 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>
#include <string_view>
 
int main()
{
    using namespace std::literals;
 
    const auto str = "Hello, C++20!"s;
 
    assert
    (""
        && str.starts_with("He"sv)  // (1)
        && !str.starts_with("he"sv) // (1)
        && str.starts_with("He"s)   // (1) implicit conversion string to string_view
        && !str.starts_with("he"s)  // (1) implicit conversion string to string_view
        && str.starts_with('H')     // (2)
        && !str.starts_with('h')    // (2)
        && str.starts_with("He")    // (3)
        && !str.starts_with("he")   // (3)
    );
}

See also

(C++20)
checks if the string ends with the given suffix
(public member function)
(C++20)
checks if the string view starts with the given prefix
(public member function of std::basic_string_view<CharT,Traits> )
(C++20)
checks if the string view ends with the given suffix
(public member function of std::basic_string_view<CharT,Traits> )
(C++23)
checks if the string contains the given substring or character
(public member function)
(C++23)
checks if the string view contains the given substring or character
(public member function of std::basic_string_view<CharT,Traits> )
compares two strings
(public member function)
returns a substring
(public member function)
Retrieved from " https://en.cppreference.com/mwiki/index.php?title=cpp/string/basic_string/starts_with&oldid=156934 "