Call external C programs and receive data

Hi,

I'd like to know if I can call a program from a program and receive result.

I've this complied C program (Called):

Code:

---

/* omissis header */

int main()
{
  int i = 0;
  i = rand();
  return i;
}

---

Can I call this program from another C program and receive "i" ?

My pseudo-code would be:

Code:

---

/* omissis */

 int dest = 0;
 dest = call Called program;

/* omissis */

---

Does the "return" instruction pass data also through compiled programs?
How to do it? How to call external programs?

Thanks

You can't do this portably.

On unix, system() (which is a standard function) will return the termination status of whatever you're running. But remember that you only get 8 bits for the return value, so you can only return values 0-255.

Again assuming unix, you could have one program print out a number and then the other program use popen() to grab the output and parse it. This is somewhat analogous to using `` or $() in the Bourne shell; it just takes a bit more work to do.

I'm not familiar with other platforms so I can't comment on them.

ShellExecuteEx and GetExitCodeProcess can do this for Windows.

Quote:

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Originally Posted by Elysia

ShellExecuteEx and GetExitCodeProcess can do this for Windows.

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popen() also works on Windows.

The 'best' way on Windows I'd say is, CreateProcess() with inherited pipes (stdout, stdin or stderr).

That means you can send more than just 1 thing, or just a number.

system() should be sufficient for getting the error/return code of the process.

And where is the result stored?

Thanks (sorry, I'm new with C)

System returns what is returned by the program it executes.

Quote:

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Originally Posted by ferenczi

And where is the result stored?

Thanks (sorry, I'm new with C)

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System returns an int.

But, I mean, if I want to use this result, where do I find it. Have I to use something like this:

Code:

---

int take = 0;
take = system("extern.exe");

---

?

Quote:

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Originally Posted by ferenczi

But, I mean, if I want to use this result, where do I find it. Have I to use something like this:

Code:

---

int take = 0;
take = system("extern.exe");

---

?

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In the example you gave, you'd find the result in the take variable. So whatever value main() returned in extern.exe is what take should equal.

Quote:

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Originally Posted by cpjust

In the example you gave, you'd find the result in the take variable. So whatever value main() returned in extern.exe is what take should equal.

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Except the case when was error starting the external program. In any case - you should read the description of system function in C-reference, especially - the return value.