为什么我的两个元组包含以相同方式创建的字符串，而不是相等的? [英] Why are my two tuples containing strings, created the same way, not equal?

问题描述

我正在使用 Microsoft Visual C++ 将以下程序编译为 C++20 程序:

I'm compiling the following program using Microsoft Visual C++, as a C++20 program:

#include <iostream>
#include <tuple>

int main()
{
    auto t1 = std::make_tuple("one", "two", "three");
    auto t2 = std::make_tuple("one", "two", "three");
    
    std::cout << "(t1 == t2) is " << std::boolalpha << (t1 == t2) << "\n";
    std::cout << "(t1 != t2) is " << std::boolalpha << (t1 != t2) << "\n";

    return 0;
}

当我运行它时，我看到以下输出:

When I run it, I see the following output:

(t1 == t2) is false
(t1 != t2) is true

元组是相同的，为什么会出现错误的比较结果?我该如何解决这个问题?

The tuples are identical, so why does it have wrong comparison results? How do I fix this?

推荐答案

您正在比较指向字符缓冲区的指针，而不是字符串.

You are comparing pointers to buffers of characters, not strings.

有时编译器会将两个不同的一个"转入同一个缓冲区，有时不会.

Sometimes the compiler will turn two different "one"s into the same buffer, sometimes it will not.

在你的情况下，它不是.可能是调试版本.

In your case, it isn't. Probably a debug build.

添加#include ，然后

using namespace std::literals;

auto t1 = std::make_tuple("one"sv, "two"sv, "three"sv);
auto t2 = std::make_tuple("one"sv, "two"sv, "three"sv);

你会得到你所期望的.(在 pre-c++17 编译器，使用 和 "s 而不是 和 ";"sv).

and you'll get what you expect. (In pre-c++17 compilers, use <string> and ""s instead of <string_view> and ""sv).

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