CODEWITHSUNDEEP
c++inter-process-communicat
Drise
Drise

Reputation: 4388

Send data to another C++ program

Is it possible to send data to another C++ program, without being able to modify the other program (since a few people seem to be missing this important restriction)? If so, how would you do it? My current method involves creating a temporary file and starting the other program with the filename as a parameter. The only problem is that this leaves a bunch of temporary files laying around to clean up later, which is not wanted.

Edit: Also, boost is not an option.

Upvotes: 3

Views: 4778

Answers (2)

Robᵩ
Robᵩ

Reputation: 168626

Clearly, building a pipe to stdin is the way to go, if the 2nd program supports it. As Fred mentioned in a comment, many programs read stdin if either there is no named file provided, or if - is used as the filename.

If it must take a filename, and you are using Linux, then try this: create a pipe, and pass /dev/fd/<fd-number> or /proc/self/fd/<fd-number> on the command line.

By way of example, here is hello-world 2.0:

#include <string>
#include <sstream>
#include <cstdlib>
#include <cstdio>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

int main () {

  int pfd[2];
  int rc;

  if( pipe(pfd) < 0 ) {
    perror("pipe");
    return 1;
  }

  switch(fork()) {
  case -1: // Error
    perror("fork");
    return 1;

  case 0: { // Child
    // Close the writing end of the pipe
    close(pfd[1]);

    // Create a filename that refers to reading end of pipe
    std::ostringstream path;
    path << "/proc/self/fd/" << pfd[0];

    // Invoke the subject program. "cat" will do nicely.
    execlp("/bin/cat", "cat", path.str().c_str(), (char*)0);

    // If we got here, then something went wrong, then execlp failed
    perror("exec");
    return 1;
  }

  default: // Parent
    // Close the reading end.
    close(pfd[0]);

    // Write to the pipe. Since "cat" is on the other end, expect to
    // see "Hello, world" on your screen.
    if (write(pfd[1], "Hello, world\n", 13) != 13)
      perror("write");

    // Signal "cat" that we are done writing
    close(pfd[1]);

    // Wait for "cat" to finish its business
    if( wait(0) < 0)
      perror("wait");

    // Everything's okay
    return 0;
  }
}

Upvotes: 4

kmarks2
kmarks2

Reputation: 4875

You could use sockets. It sounds like both application are on the same host, so you just identify the peers as localhost:portA and localhost:port B. And if you do it this way you can eventually graduate to do network IO. No temp files, no mystery parse errors or file deletions. TCP guarantees packet delivery and guarantees they will be ordered correctly.

So yeah, I would consider creating an synchronous socket server (use asynchronous if you anticipate having tons of peers). One benefit over pipe oriented IPC is that TCP sockets are completely universal. Piping varies dramatically based upon what system you are on (consider Windows named pipes vs implicit and explicit POSIX pipes -> very different).

Upvotes: 1

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