为什么 ofstream 需要刷新?

如果我运行以下代码，则根本不会创建任何文件:

std::ofstream outputFile(strOutputLocation.c_str(), std::ios::binary);outputFile.write((const char*)lpResLock, dwSizeRes);outputFile.close();

但是，如果我在关闭之前添加一个flush()，它会起作用:

std::ofstream outputFile(strOutputLocation.c_str(), std::ios::binary);outputFile.write((const char*)lpResLock, dwSizeRes);outputFile.flush();outputFile.close();

标准库是否真的需要这个，还是 Visual C++ CRT 中的一个错误?

解决方案

这是一个错误.阅读第 27.8.1.10/4 节，删节:

<块引用>

void close();
效果:调用 rdbuf()->close()...

rdbuf()->close() 有什么作用?根据第 27.8.1.3/6 节，删节，强调我的:

<块引用>

basic_filebuf* close();
如果 is_open() == false，则返回空指针.如果放置区域存在，则调用overflow(EOF)来刷新字符. ...

也就是说，它应该刷新.(实际上，对 flush() 的调用最终会做同样的事情.)

<小时>

请注意，不需要调用 close() 本身，因为 basic_ofstream 的析构函数将调用 close().

If I run the following code, no file is created at all:

std::ofstream outputFile(strOutputLocation.c_str(), std::ios::binary);
outputFile.write((const char*)lpResLock, dwSizeRes);
outputFile.close();

However, if I add a flush() before the close, it works:

std::ofstream outputFile(strOutputLocation.c_str(), std::ios::binary);
outputFile.write((const char*)lpResLock, dwSizeRes);
outputFile.flush();
outputFile.close();

Does the standard library actually require this, or is it a bug in the Visual C++ CRT?

解决方案

It's a bug. Reading §27.8.1.10/4, abridged:

void close();
Effects: Calls rdbuf()->close()...

What does rdbuf()->close() do? According to §27.8.1.3/6, abridged, emphasis mine:

basic_filebuf<charT,traits>* close();
If is_open() == false, returns a null pointer. If a put area exists, calls overflow(EOF) to flush characters. ...

That is, it's suppose to flush. (Indeed, the call to flush() ultimately does the same thing.)

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Note the call to close() itself isn't needed, as the destructor of basic_ofstream will call close().