Reading gcc output in a string

Question

If we execute gcc to compile a source file through the system() function, how can I capture the gcc output in a string ?

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I tried with popen which works as long as it reads something like "PAUSE", but did not work with gcc as it runs a new child process.

Answer 1

There are many ways.

Simple way: Redirect the output to a temporary file and read the temporary file into a string.

You can use pipes. In the child process, redirect the output to pipe and read from the other end of the pipe into a string. See man pipe

//In the parent process
int fd[2]
pipes(fd);

//Use fork+execv instead of system to launch child process.
if (fork()==0) {
    //Redirect output to fd[0]
   dup2(fileno(fd[0]), STDOUT_FILENO);
   dup2(fileno(fd[0]), STDERR_FILENO);
   //Use execv function to load gcc with arguments.

} else {
  //read from the other end fd[1]
}

See thread at http://ubuntuforums.org/archive/index.php/t-1627614.html.

Also see In C how do you redirect stdin/stdout/stderr to files when making an execvp() or similar call?

For Windows, this link might help you. https://msdn.microsoft.com/en-us/library/windows/desktop/ms682499%28v=vs.85%29.aspx Flow is almost same as Linux. Syntax and primitives might be different. Here, idea is to use Pipe and redirect process output files to your pipe file.

Answer 2

If you are attempting to read the error messages produced by gcc, you need to remember that they are sent to stderr, not stdout. popen captures stdout but does not redirect stderr.

If system on Windows provides a standard posix shell, you could redirect stderr to stdout in the command line you provide to popen, by adding the redirection 2>&1.