CODEWITHSUNDEEP
c++ccommand
Real Red.
Real Red.

Reputation: 5049

How to read/redirect output of a dos command to a program variable in C/C++?

I want to run a dos command from my program for example "dir" command. I am doing it like, 

system("dir");

Is there any way to read the output of that command directly into a program variable?

We can always redirect the output to a file and then read that file, by doing
system("dir > command.out");

And then reading command.out file. But how can we do it directly rather than redirectling to a file and then reading?

Upvotes: 4

Views: 4945

Answers (5)

Loki Astari
Loki Astari

Reputation: 264739

Use popen() it does exactly what you want.
It creates a bidirectional pipe, forks the processes. In the child it then connects the pipe to standard in and standard out then execs the command specified as the first parameter to popen().

#include <stdio.h>
#include <string>
#include <iostream>

int main()
{
    std::string     output;
    FILE*           data    = popen("cat PLOP","r");

    for(char c = getc(data);c != EOF;c = getc(data))
    {
        output  += c;
    }
    pclose(data);

    std::cout << "Data(" << output << ")\n";
}

Upvotes: 0

Real Red.
Real Red.

Reputation: 5049

Found an alternate way or rather windows equivalent of popen. It is _popen(). This works just right for me and moreover it's easy to use.

   char   psBuffer[128];
   FILE   *pPipe;

   if( (pPipe = _popen( "dir", "rt" )) != NULL)
  {
     while(fgets(psBuffer, 128, pPipe))
     {
       printf(psBuffer);
     }
  }

Find the details with full example here.

Upvotes: 4

qrdl
qrdl

Reputation: 35008

If your library has popen() POSIX function, that's what you need. You can read command output from pipe and parse it any way you like.

FILE *dir;
char direntry[80];

dir = popen("dir", "r");
while (!feof(dir)) {
    fgets(direntry, sizeof(direntry), dir);
    /* do something with direntry */
}

Upvotes: 4

unwind
unwind

Reputation: 400159

You can't. The programs run in different memory spaces, as they are different processes. Generally, in modern operating systems, processes don't share memory.

Also, it would be difficult to define a variable in C that can hold the output of a command such as "dir"; it's would need to dynamically grow to make room.

The best way is to use a pipe, that will make it possible to read the command's output from a stream, from which you can store it as you see fit.

Upvotes: 1

sharptooth
sharptooth

Reputation: 170569

You can't redirect it to a variable, but you can do a trick similar to how pipes are used in Unix for chaining commands. Call CreateProcess(), and pass it a STARTUPINFO instance with accordingly set handles and STARTF_USESTDHANDLES in STARTUPINFO::dwFlags. Then read the data coming from the spawned process through the set handles.

Upvotes: 4

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