windows 我可以使用 CreateFile，但将句柄强制转换为 std::ofstream 吗？
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Can I use CreateFile, but force the handle into a std::ofstream?
提问by Steve Folly
Is there any way to take advantage of the file creation flags in the Win32 API such as FILE_FLAG_DELETE_ON_CLOSEor FILE_FLAG_WRITE_THROUGHas described here http://msdn.microsoft.com/en-us/library/aa363858(VS.85).aspx, but then force that handle into a std::ofstream?
有什么方法可以利用 Win32 API 中的文件创建标志，例如FILE_FLAG_DELETE_ON_CLOSE或FILE_FLAG_WRITE_THROUGH如此处所述http://msdn.microsoft.com/en-us/library/aa363858(VS.85).aspx，然后强制将句柄转换为 std::ofstream？
The interface to ofstream is obviously platform independent; I'd like to force some platform dependent settings in 'under the hood' as it were.
ofstream 的接口显然是平台无关的；我想在“幕后”中强制一些平台相关的设置。
回答by ChrisN
It is possible to attach a C++ std::ofstreamto a Windows file handle. The following code works in VS2008:
可以将 C++ 附加std::ofstream到 Windows 文件句柄。以下代码适用于 VS2008：
HANDLE file_handle = CreateFile(
file_name, GENERIC_WRITE,
0, NULL, CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL, NULL);
if (file_handle != INVALID_HANDLE_VALUE) {
int file_descriptor = _open_osfhandle((intptr_t)file_handle, 0);
if (file_descriptor != -1) {
FILE* file = _fdopen(file_descriptor, "w");
if (file != NULL) {
std::ofstream stream(file);
stream << "Hello World\n";
// Closes stream, file, file_descriptor, and file_handle.
stream.close();
file = NULL;
file_descriptor = -1;
file_handle = INVALID_HANDLE_VALUE;
}
}
This works with FILE_FLAG_DELETE_ON_CLOSE, but FILE_FLAG_WRITE_THROUGHmay not have the desired effect, as data will be buffered by the std::ofstreamobject, and not be written directly to disk. Any data in the buffer will be flushed to the OS when stream.close()is called, however.
这适用于FILE_FLAG_DELETE_ON_CLOSE，但FILE_FLAG_WRITE_THROUGH可能不会达到预期的效果，因为数据将由std::ofstream对象缓冲，而不是直接写入磁盘。但是，缓冲区中的任何数据都会在stream.close()调用时刷新到操作系统。
回答by Rolf Kristensen
Some of these flags are also available when using _fsopen / fopen:
使用 _fsopen / fopen 时，其中一些标志也可用：
FILE* pLockFile = _fsopen(tmpfilename.c_str(), "w", _SH_DENYWR );
if (pLockFile!=NULL
{
// Write lock aquired
ofstream fs(pLockFile);
}
Here we open the file so when doing a flush, then it writes through (And it is deleted when closed):
在这里，我们打开文件，以便在进行刷新时，然后写入（关闭时将其删除）：
FILE* pCommitFile = fopen(tmpfilename.c_str(), "wcD");
if (pCommitFile!=NULL)
{
// Commits when doing flush
ofstream fs(pCommitFile);
}
