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

 

C++

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自由（freestanding）与宿主（hosted）

语言

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标准库头文件

具名要求

特性测试宏 (C++20)

语言支持库

概念库 (C++20)

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元编程库 (C++11)

通用工具库

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技术规范

符号索引

外部库

 

字符串库

类

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

成员函数 basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23)   basic_string::get_allocator 元素访问 basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) 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) 搜索 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

修改器 basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::replace basic_string::replace_with_range (C++23) basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)  basic_string::swap 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 (DR*) 操作 basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::substr

常量 basic_string::npos 非成员函数 operator+ swap(std::basic_string) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline 比较 operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) 数值转换 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) 字面量 operator""s (C++14) 辅助类 hash<std::basic_string> (C++11) 推导指南 (C++17)

 

bool empty() const;		(C++11 起无异常抛出) (C++20 起为 constexpr)

检查字符串是否不包含任何字符，即 begin() == end()。

参数

(无)

返回值

如果字符串为空，则为 true，否则为 false

复杂度

常数时间。

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

sizelength	返回字符数 (public member function)
max_size	返回字符的最大数量 (public member function)
capacity	返回当前分配存储中可容纳的字符数 (public member function)
sizessize (C++17)(C++20)	返回容器或数组的大小 (function template)
empty (C++17)	检查容器是否为空 (function template)
empty	检查视图是否为空 (std::basic_string_view<CharT,Traits> 的公共成员函数)