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std::ignore

STD：忽略

Defined in header ​​
const /*unspecified*/ ignore;​(since C++11) (until C++17)
inline constexpr /*unspecified*/ ignore;​(since C++17)

一种未指定类型的对象，可以将任何值赋值给它，而不产生任何效果。打算与...一起使用std::tie当解压时std::tuple，作为未使用的参数的占位符。

例

解压缩set.INSERT%28%29返回的一对，但只保存布尔值。

二次

#include <iostream>
#include <string>
#include <set>
#include <tuple>
 
int main()
{
    std::set<std::string> set_of_str;
    bool inserted;
    std::tie(std::ignore, inserted) = set_of_str.insert("Test"
    if (inserted) {
        std::cout << "Value was inserted successfully\n";
    }
}

二次

产出：

二次

Value was inserted successfully

二次

tiecreates a tuple of lvalue references or unpacks a tuple into individual objects (function template)

 © cppreference.com

在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。

http：//en.cppreference.com/w/cpp/实用程序/tuple/忽略

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