Get the output of one C program into a variable in another C program

Question

I have 2 C programs. Say one is program-1.c

int main(){
printf("hello world");
}

Now in 2nd code named program-2.c, I want the output of 1st code into a variable, so that I can have the output "hello world" into a variable in the 2nd C code.

How can I do this?

Solution 1

You can use the popen function for this:

FILE* proc1 = popen("./program1", "r");
// Usual error handling code goes here
// use the usual FILE* read functions
pclose(proc1);

Solution 2

You will need to run the two programs in two separate processes and then use some sort of IPC mechanism to exchange data between the two processes.

Solution 3

On many operating systems you can get the output from one console program as input to the next, perhaps

program-1 > program-2

you can then read the result from standard input

std::string  variable;

std::getline(std::cin, variable);

Solution 4

Sample Code for "Output of one program is input of another program Using Pipes"

#include <unistd.h>
#include <process.h>

/* Pipe the output of program to the input of another. */

int main()
{
  int pipe_fds[2];
  int stdin_save, stdout_save;

  if (pipe(pipe_fds) < 0)
    return -1;

  /* Duplicate stdin and stdout so we can restore them later. */
  stdin_save = dup(STDIN_FILENO);
  stdout_save = dup(STDOUT_FILENO);

  /* Make the write end of the pipe stdout. */
  dup2(pipe_fds[1], STDOUT_FILENO);

  /* Run the program. Its output will be written to the pipe. */
  spawnl(P_WAIT, "/dev/env/DJDIR/bin/ls.exe", "ls.exe", NULL);

  /* Close the write end of the pipe. */
  close(pipe_fds[1]);

  /* Restore stdout. */
  dup2(stdout_save, STDOUT_FILENO);

  /* Make the read end of the pipe stdin. */
  dup2(pipe_fds[0], STDIN_FILENO);

  /* Run another program. Its input will come from the output of the
     first program. */
  spawnl(P_WAIT, "/dev/env/DJDIR/bin/less.exe", "less.exe", "-E", NULL);

  /* Close the read end of the pipe. */
  close(pipe_fds[0]);

  /* Restore stdin. */
  dup2(stdin_save, STDIN_FILENO);

  return 0;
}

Cheers....

Solution 5

In the code for the program-2.c you should use int argc and char *argv[] to get the output from program-1.c

So program-2.c should look like this:

void main(int argc, char *argv[]) 
{
   int i;

   for( i=0; i<argc; i++ ) 
   {
        printf("%s", argv[i]); //Do whatever you want with argv[i]
   }       

}

Then in the command prompt program-1 > program-2

View more solutions

Comments

[stijn]

+1 as IPC is almost always the better and scalable solution, unless the two programs are purely for procesing text.

[Shamim Hafiz - MSFT]

But won't that restrict input from program-1 only? I think if one was simply interested to fetch the output from one running program and be still able to switch around standard input, this method may not be ideal.

[Bo Persson]

Right. We don't have any info on how the programs are to be run, so this is just one possible solution (assuming console programs on Windows/Linux).

[Ronin]

thank u all ... but I am looking for this solution in WINDOWS ... Can u plz help ??

[Ronin]

thank u all ... but I am looking for this solution in WINDOWS ... Can u plz help ??

[Mat]

stackoverflow.com/questions/450865/…

[EHM]

Thank you for the answer. why wouldnt piping work here