std::basic_string::empty

 

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std::basic_string

成员函数 basic_string::basic_string basic_string::operator= basic_string::assign basic_string::get_allocator 元素访问 basic_string::at basic_string::operator[] basic_string::front (C++11) basic_string::back (C++11) basic_string::data basic_string::c_str basic_string::operator basic_string_view (C++17) 迭代器 basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) 容量 basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (C++11)

操作 basic_string::clear basic_string::insert basic_string::erase basic_string::push_back basic_string::pop_back (C++11) basic_string::append basic_string::operator+= basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::replace basic_string::substr basic_string::copy basic_string::resize basic_string::swap 查找 basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of 常量 basic_string::npos

非成员函数 operator+ operator==operator!=operator<operator>operator<=operator>= swap(std::basic_string) operator<<operator>> getline stoistolstoll (C++11) (C++11) (C++11) stoulstoull (C++11) (C++11) stofstodstold (C++11) (C++11) (C++11) to_string (C++11) to_wstring (C++11) operator""s (C++14) 辅助类 hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string> (C++11) (C++11) (C++11) (C++11) hash<std::pmr::string>hash<std::pmr::wstring>hash<std::pmr::u32string>hash<std::pmr::u16string> (C++20) (C++20) (C++20) (C++20) 推导指引(C++17)

 

bool empty() const;		(C++20 前)
[[nodiscard]] bool empty() const;		(C++20 起)

检查 string 是否无字符，即是否 begin() == end() 。

参数

（无）

返回值

若 string 为空则为 true ，否则为 false 。

异常

（无）	(C++11 前)
noexcept 规定：   noexcept	(C++11 起)

复杂度

常数。

示例

运行此代码

#include <iostream>
#include <string>
 
int main()
{
    std::string s;
    std::boolalpha(std::cout);
    std::cout << "s.empty():" << s.empty() << "\t s:'" << s << "'\n";
 
    s = "Exemplar";
    std::cout << "s.empty():" << s.empty() << "\t s:'" << s << "'\n";
 
    s = "";
    std::cout << "s.empty():" << s.empty() << "\t s:'" << s << "'\n";
}

输出：

s.empty():true	 s:''
s.empty():false	 s:'Exemplar'
s.empty():true	 s:''

参阅

size length

返回字符数 (公开成员函数)