From:	"Rafał Maj" <r_maj AT poczta DOT onet DOT pl>
Newsgroups:	comp.os.msdos.djgpp
Subject:	calling functions
Date:	Wed, 16 Aug 2000 10:44:44 +0200
Organization:	Academic Computer Center CYFRONET AGH
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

My small program is making a copy of code of some function. Program works
fine, until my function is trying to call
library functions.

================ THIS PROGRAM WORKS ====================
#include <iostream.h>
int globA, globB, globC;

void fun() { globC= globA + globB; }
void fun_end() {};

main() {
  globA=10; globB=5;

  long int size = ((long int)(void*)fun_end) - ((long int)(void*)fun);
  char *ptr = new char[size];
  memcpy(ptr,(void*)fun,size);

  void (*function_ptr)() = (void (*)()) ptr;

  (*function_ptr)();  // <------ CALL of function copy
  cerr<<globC<<endl; // same as print()
}


================ THIS PROGRAM DOESN'T WORK ====================
#include <iostream.h>
#include <dos.h>
int globA, globB, globC;

void fun() { globC= globA + globB;
  delay(10); // <-------------------------- library function
}
void fun_end() {};

main() {
  globA=10; globB=5;

  long int size = ((long int)(void*)fun_end) - ((long int)(void*)fun);
  char *ptr = new char[size];
  memcpy(ptr,(void*)fun,size);

  void (*function_ptr)() = (void (*)()) ptr;

  (*function_ptr)();  // <------ program crashes (with error code 255)
  cerr<<globC<<endl; // same as print()
}

===============================================================
So, can You send me working example, how to call copy of functions ?
I know it's possible, because Allegro is using stuf like this.

Rafal

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