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From: "Robbie Hatley" <loneXwolfintj AT pacXbell DOT net DOT remove DOT Xs>
Newsgroups: comp.os.msdos.djgpp
References: <4017ddaa$1_6 AT Newsfeeds DOT com> <401875b6 DOT 1196777 AT news DOT voyager DOT net>
Subject: Re: How do I feed output of DOS commands into a program?
Date: Mon, 2 Feb 2004 05:05:23 -0800
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"Chris Giese" <NoEmailAds AT execpc DOT com> wrote in message news:401875b6 DOT 1196777 AT news DOT voyager DOT net...
> "Nathan Kreiger" <nathankreiger AT hotmail DOT com> wrote:
>
> >Greetings, group.  I'm writing a program in C++ and compiling with
> >DJGPP's gxx, and I'd like to be able to run DOS commands such
> >as "CD" (get current directory) and funnel the result back into my
> >program, without using temporary files.  I could always do:
>
> Use popen() and pclose():
>
> #include <stdio.h>
> int main(void) {
> static char buf[8000];
> FILE *pipe = popen("CD", "r");
> (void)fread(buf, 1, sizeof(buf), pipe);
> pclose(pipe);
> printf("%s", buf);
> return 0; }

That's very interesting, but doesn't really constitute "not using
temporary files".  However, I do thank you for your answer, because
it lead to me reading the documentation for the popen() and pclose()
functions, which I had never heard of before.  I read a comment in
there to the effect that "temporary files must be used because
DOS is not a multitasking operating system".  Ie, what I was
trying to do is apparently impossible.

So, I re-wrote my program so that it no-longer needs to determine
current directory through use of system("CD > tempfile.tmp") ;
instead, I test for success or failure of changing current directory:

ErrorFlag = chdir(TargetDir.c_str());  // TargetDir is a std::string
if (ErrorFlag)
{
    cerr << "oops" << endl;
    exit (1);
}

That way I can navigate directory trees recursively without using
any temporary files (either explicit or implicit, judging by lack of
activity of IDE LED), and still have error-checking on whether
current-directory-changes were successful.  (This is program
that seeks-out and erases duplicate files.)

RH




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