Question

I have a Windows C++ program that is doing something like:

   FILE* pf = ...;   *stdout = *pf;    // stdout is defined in stdio.h 

I’m looking for an explanation about what happens when you change the value of the stdout file handle. Is this just a way of redirecting stdout?

-cr

Answer 1

If you change stdout by assignment instead of by using the tool designated (in C, freopen() as Adam Rosenfield said – and by extension, in C++), then you leave yourself open to all sorts of liabilities.

• It is not clear that cout will also be redirected.
• You will likely leak a file descriptor (which may not matter).
• You might not flush the original stdout properly – losing information.
• You might leak memory associated with the original file pointer (which again may not matter).
• If anything closes pf, then you are liable for double-free errors (crashes).

It is far better to do the job cleanly.

(Demo code isn’t necessarily written by, or even scrutinized by, the most experienced people in a vendor’s coding team. If it looks dubious, that may be because it is dubious.)