how to use isatty() on cout, or can I assume that cout == file descriptor 1?

Question

Well, the subject says it all, basically.

I have a command-line utility that may be used interactively or in scripts, using pipes or i/o redirection. I am using

Answer 1

It is possible to use rdbuf() to change the destination of std::cin and std::cout inside your program. If you don't do that, it is probably quite safe to assume that cin = 0, cout=1 and clog and cerr both = 2 as the C++ standard states that they are synchronized with C stdin, stdout and stderr and those have per POSIX those file descriptors at startup.

Answer 2

If using Linux (and probably other unixes, but definitely not Windows) you could try isatty.

There's no direct way of extracting the file descriptor from the C++ stream. However, since in a C++ program both cout as well as stdout exist and work at the same time (C++ by default provides synchronisation between stdio and iostream methods), your best bet in my opinion is to do a isatty(fileno(stdout)).

Make sure you #include <unistd.h>.