Question

I want to write two c++ application the first one called “caller,” the second called “processor.”

caller application send a value to a processor. after that processor do some process on that value and return it back to caller.

I want to know the best way to do that.

so far I know how to send value from caller application to processor application but I could not find any way to return the value back. one of this way by using putenv() and getenv()

caller example

#include <iostream>
#include <stdlib.h>

using namespace std;

int main(int argc, char **argv, char** envp){
    char myvar[]="MYVAR= say something";
    putenv(myvar);
    cout<<getenv("MYVAR")<<endl;
    system("./processor");
    cout<<getenv("MYVAR")<<endl;
}

processor example

#include <iostream>
#include <stdlib.h>

using namespace std;

int main(int argc, char **argv, char** envp){
    char myvar[]="MYVAR= say something else";
    putenv(myvar);
    cout<<getenv("MYVAR")<<endl;
}

how to fix that to return value from processor to caller and if there is better way what is it. I am using Ubunut OS.

Answer 1

There are many possible ways to communicate between to processes, and which is best depends on a lot of factors. Using the environment is basically only good for one-way communication, not bidirectional communication. The methods available include:

• Environment variables (one way)
• Command-line arguments (one way)
• Pipes
• Files
• Sockets
• FIFOs
• Shared memory
• Message queues
• Signals
• Semaphores

Some are limited to processes connected by a common ancestor; others can work between unrelated processes, sometimes not even on the same machine. Some mechanisms can communicate very little data (signals, for example); others can communicate large quantities of data. Some require no synchronization; others require extensive synchronization.

Which is best for you? We don’t have enough information to guess. However, your best choice is most likely between pipes, files and sockets.