PortableFtruncate

WindowsLinuxPortability

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ftruncate for Win32

fd から HANDLEへの変換には、VCなら _get_osfhandleが使える。

// If you are using Visual C++, you can use _get_osfhandle() (declared in <io.h>)
// to convert a file descriptor (int) into a file handle (HANDLE)
int ftruncate(HANDLE hFile, long long size)
{
	LARGE_INTEGER currentpos, pos, newpos;
 
	// save current position
	pos.QuadPart = 0;
	if (!SetFilePointerEx(hFile, pos, &currentpos, FILE_CURRENT)) {
	  return -1;
	}
 
	// move to new position
	pos.QuadPart = size;
	if (!SetFilePointerEx(hFile, pos, &newpos, FILE_BEGIN)) {
	  return -1;
	}
 
	// change file size
	if (!SetEndOfFile(hFile)) {
	  return -1;
	}
 
	// ...and return to the original position
	// (the file pointer is not changed by ftruncate on POSIX systems.)
	if (!SetFilePointerEx(hFile, currentpos, &newpos, FILE_BEGIN)) {
	  return -1;
	}
 
	return 0;
}