！=操作符和文件流 [英] != operator and file streams

问题描述

#include <iostream>
#include <fstream>

using namespace std;

int main()
{

    ifstream file0( "file0.txt" );
    ifstream file1( "file1.txt" );

    if (file0 != file1) {
        cout << "What is being compared?" << endl;
    }

} 

如果上述代码，在条件？我相信这是指针值，但我无法找到支持证据。

If the above code, what is being compared in the conditional? I believe it is pointer values but I am unable to find supporting evidence.

谢谢！

推荐答案

当对ifstream进行比较时，将调用 operator void * 。如果你使用visual studio，你可以看到这个，如果你选择看到反汇编的代码。

When doing a comparison on an ifstream the operator void* will be called. If you are using visual studio you can see this if you choose to see the disassembly of the code.

可以找到操作符此处。
正如你可以看到的那样：

The operator can be found here. As you can see mentioned:

返回的指针不是要被引用，错误标志设置。

The pointer returned is not intended to be referenced, it just indicates success when none of the error flags are set.

因此，如果两个ifstreams失败，它们将是相等的。如果他们成功了（虽然我不知道指针值来自哪里），他们将不相等[这已经在VS上测试]。

So if both ifstreams fail, they will be equal. If they succeed (although I am not sure where the pointer value comes from) they will not be equal [this has been tested on VS].

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