如果调用了fclose(0)，这会关闭stdin吗? [英] If fclose(0) is called, does this close stdin?

问题描述

如果调用了fclose(0)，这会关闭stdin吗?

If fclose(0) is called, does this close stdin?

之所以这样问，是因为某种原因，stdin在我的应用程序中被关闭了，我无法弄清原因.我检查了fclose(stdin)，但它不在应用程序中，所以我想知道fclose(0)是否会导致未定义的行为，例如关闭stdin?

The reason why I'm asking this is that for some reason, stdin is being closed in my application and I cannot figure out why. I checked for fclose (stdin) and this is not in the application and so I was wondering if fclose(0) could cause undefined behaviour such as closing stdin?

如果没有，stdin可能被错误关闭的其他方式是什么?

If not, what are other ways that stdin could be erroneously closed?

推荐答案

fclose的签名是这样:

int fclose ( FILE * stream );

这意味着，fclose需要一个指向FILE对象的指针.因此，如果传递0而不是指针，则将0理解为NULL指针 ¹ .如果它为NULL指针，您如何期望它关闭stdin?它不会关闭.使用fclose(stdin)，因为stdin本身是指向FILE对象的指针.

That means, fclose expects a pointer to FILE object. So if you pass 0, instead of a pointer, 0 would be understood as NULL pointer¹. If its NULL pointer, how do you expect it to close stdin? It will not close. Use fclose(stdin), as stdin itself is a pointer to FILE object.

我认为您将stdin与文件描述符(其为整数类型，通常表示为fd)混淆.输入流的fd是0是正确的.因此，如果要使用fd(而不是FILE*)，则必须使用<unistd.h>中的close.

I think you're confusing stdin with file-descriptor which is of integral type, and usually denoted as fd. Its true that fd of input stream is 0. So if you want to use fd (instead of FILE*), then you've to use close from <unistd.h>.

#include <unistd.h>
int close(int fildes);

也就是说，close(0)将关闭标准输入.

That is, close(0) would close stdin.

_{1:似乎很有趣，如果您已通过1传递给fclose并打算关闭stdout，则您的代码甚至无法编译，并且您会在编译时立即看到代码问题.现在的问题是，为什么不编译?因为与0不同，1不会隐式转换为指针类型.编译器将生成类似"error: invalid conversion from ‘int’ to ‘FILE*’的消息.请在ideone上查看错误和行号此处.}

_{1 : It seems interesting that if you had passed 1 to fclose with the intention to close stdout, your code wouldn't even compile, and you would immediately see the problem with your code at compile-time itself. Now the question is, why would it not compile? Because unlike 0, 1 is not implicitly converted into pointer type. The compiler would generate message like "error: invalid conversion from ‘int’ to ‘FILE*’. See the error and line number here at ideone.}

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