title: Qt/C++ (Pre-)Allocating large file
body: <p>Is there a way of allocating a file with a determined size with Qt?</p>
  
  <p>The reason is to avoid or minimize fragmentation. I don't want to zero-write a large file (unwanted overhead), but just allocate it from the file system.</p>
  
  <p>I'd like a solution which works on Win/OSX/Linux. I know there are solutions depending on the file system in question for all these platforms, but digging up the solutions and testing on each platform takes some time.</p>