Is setting a FILE* equal to stdout portable?

问题:

I've got a function that needs to be able to write to either stdout, or to a file, depending on what the user wants. It defaults to standard out though. To accomplish this, I'm doing the following (minus error checking etc):

FILE* out;
if (writeToFile) { /*Code to open file*/; }

else
    out = stdout;

// ...rest of the function goes here

if (out != stdout)
    fclose(out);

This certainly does the trick, but I have no idea how portable it is. And if it's not, and/or there's another problem with it, how should I go about this?

回答1:

Yes, it's portable and it's fine, provided you don't also mess with the low-level implementation of *stdout (e.g. by calling close(fileno(stdout)) on Posix or using dup).

回答2:

It should be fine. You might have trouble if you pass the pointer back and forth across the boundary of a DLL (ie, C code outside DLL passes pointer to stdout to C code inside DLL), but apart from that it should be portable.