how to pass variable argument to exe?

Question

Okay, let's say that I have b.exe, which takes a string argument. I want to invoke b.exe within a.cpp, with system:

    string s1 = "hallo";
    system("b.exe s1");
    printf("s1 after invoke = %s",s1);

and this is the code in b.cpp:

    int main(string s)
    {
         s = "hello world";
         return 0; 
    }

what I want is, when I run a.exe, the output will be:

    s1 after invoke = hello world

is it possible to do that? basically, i just want to pass a variable to an exe, but it must be by reference, not only by value because I want that variable to be processed and modified within the exe that I invoked. I've already searched the solution on the internet, but it only provides me tha way to pass a variable by value to the exe, not by reference..

any suggestion will be very appreciated, but if possible, I want the suggestion in the form of the above correction code and include files, if any. thanks for your help :)

A classical question on communication between processes! A simple solution is to share memory between the two processes. If you are using Linux, please search `mmap()` and see example programs. :-) — Stan, Jul 23 '11 at 07:37

score 3 · Accepted Answer · answered Jul 23 '11 at 06:55

3

It is not possible to modify command line arguments among different processes. s1 is known only to A.CPP, and s is only known to B.CPP.

answered Jul 23 '11 at 06:55

Ajay

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Alphanumu · Answer 2 · 2013-08-26T01:04:42.527

Hi guys I know this is an old post but every little helps :)

Sending a argument to an externally called .exe using a variable can easily be done by appending a string variable to use for the system call using .c_str()

After reading back the original question its seems the the guy wants to take a variable from within an .exe which is not possible but for what I was searching for and since this is the first Google link that is returned and I think many others will benefit from this so..

Example:

// declare some variables

void runapp();

string ip;
string img;
string tri = "notepad.exe";
string loadexe;
string space =  " "; //Just a simple ascii space used between arguments

// compile your string for the system call

    ip = argv[1];
    img = argv[2];

    loadexe = tri + space + ip + space + img; // compiled string to use for system call

//call your .exe

system(loadexe.c_str());

//full source below

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

using namespace std;

void runapp();

string ip;
string img;
string tri = "notepad.exe"; // your .exe to load
string loadexe;
string space =  " "; //Just a simple ascii space used between arguments

void main(int argc , char *argv[])
{   
    ip = argv[1];
    img = argv[2];

    loadexe = tri + space + ip + space + img;

    }else{
        //bla bla bla
}

void runapp()
{
    system(loadexe.c_str());
}

Regards

Alphanu

K Mehta · Answer 3 · 2011-07-23T07:03:39.690

No, that's not possible. Also, main does not accept string as a parameter.

your string s1 is in the address space of the process which holds a.cpp. You cannot pass items by reference between processes, which is what you're trying to achieve when passing s1 to process running b.exe. Here's what will happen when you fix your syntax errors: b.exe copies the contents of the string, saving them in its own address space.

You'll want to look into inter-process communication to achieve something similar, but there's no easy way of doing it.

score 0 · Answer 4 · answered Jul 23 '11 at 06:55

It is not possible to do that. The best you can do is pass strings by value. And by strings, I really mean char arrays.

In fact, the official prototype for main is more like

int main(int argc, char** argv);

If you want your program to compile in C++, you don't have much choice

score 0 · Answer 5 · answered Jul 23 '11 at 06:56

Your main(string) syntax is not correct. In C++ main can have two valid signatures:

int main ();
int main (int argc, char **argv);

Where argc contains the number of argument passed to the executable and argv points to the array of those arguments.

You can pass several argument to b.exe and write your program based on that. For more info you can search for signature of main() and how it is used.

score 0 · Answer 6 · answered Jul 23 '11 at 07:09

A simple, but of course, not the prettiest solution, would be to use a temporary file:

Pseudo code: Call A) Do everything in A) that you need before you call B). From A), Output variables to a temporary file. From A), call B. Import variables from temporary file. Clear this file. Do everything that you need to do in B) Output variables from B) to temporary file Exit B) Input variables from temporary file to A) Do standard output Exit A)

Otherwise you'll need to look into Message Passing Interface (M.P.I.), which is not exactly the easiest solution.

score 0 · Answer 7 · answered Jul 28 '11 at 07:35

It's not possible to modify a variable directly between two processes, but you can do something similar to get the same end result.

Simplest way of doing this might be to use _popen(). Basic idea is this:

To pass a string argument from A to B, you can pass it as a command line parameter. B can read this from the argv[] array in main().
But to return information back to B, you need some other technique. _popen() uses pipes internally, and does much of the work of setting it up for you, so A can then use fgets() or any other FILE*-based function to read the output back from B. B can then do printf("hello world"); to 'return' the string, and A can read that string from the FILE* that _popen() returns.

See the MSDN page on _popen() for more details and an example.

how to pass variable argument to exe?

7 Answers7