[SOLVED] subprogram called at run time

piobair · 07-30-2018, 02:17 PM

I have an embedded program (runs in continuous loop) that needs to call one of several subprograms, depending on circumstances. I don't need to have the subprograms loaded in memory permanently.
So, the following program represents the embedded program:

Code:

// test.c
#include<stdio.h>

int main(){
  struct {int i, j; float x, y; char *string;}subinput;
  int i;
  subinput.i = 7;
  subinput.j = 11;
  subinput.x = 3.14159;
  subinput.y = 13.4567;
  subinput.string = "Hello world";
  
  i = execve("subprog", &subinput, "./");
  printf("i = %d\n", i);
}

and here is its subprogram:

Code:

 //subprog.c
#include<stdio.h>
#include<stdlib.h>

typedef struct common common;

int main(struct common {int i, j; float x, y; char *string;} *input){
  printf("You are here\n");
  printf("i = %d, j = %d, x = %f, y = %f, string = %s!\n", input->i, input->j, input->x, input->y, input->string);
  return(3);
}

test prints "i = -1".
Suggestions?

Keith Hedger · 07-30-2018, 02:38 PM

See this in the man pages

Code:

...
execve() does not return on success, and the text, initialized data, uninitialized data (bss), and stack of the calling process are overwritten according to the contents of the newly loaded program.
...

When I need to run and get data from an external program I use the 'popen' call.

NevemTeve · 07-30-2018, 02:52 PM

Also main's parameters ('int argc' and 'char **argv) are predefined, you cannot re-define them.

piobair · 07-30-2018, 04:53 PM

Well, phooey.
Thank you.

Quote:

Originally Posted by NevemTeve

Also main's parameters ('int argc' and 'char **argv) are predefined, you cannot re-define them.