getvect function is undefined

Question

I am trying to run this program. It uses the interrupts and when we press w, it replace it by s in keyboard buffer

#include "stdafx.h"
#include "stdio.h"
#include "bios.h"
#include <dos.h>


void interrupt_oldint15(*oldint15);
void interrupt_newint15(unsigned int BP, unsigned int DI, unsigned int SI, unsigned int DS, 
                        unsigned int ES, unsigned int DX, unsigned int CX, unsigned int BX,
                        unsigned int AX, unsigned int IP, unsigned int CS, unsigned int flags);
void main ( )
{

oldint15 = getvect (0x15);
setvect (0x15, newint15);
keep (0, 1000);
}
void interrupt_newint15 (unsigned int BP, unsigned int DI, unsigned int SI, unsigned int DS, unsigned int ES, unsigned int DX, unsigned int CX, unsigned int BX, unsigned int AX, unsigned int IP, unsigned int CS, unsigned int flags )
{
if(*((char*)&AX)==0x11)
*((char*)&AX)=0x1F;
else if(*((char*)&AX)==0x1F)
*((char*)&AX)=0x11;

}

but it gives the error in getvect and setvect functions.

Answer 1

for one thing, interrupt functions, in C, do not have parameters, nor a returned value.
Listing all the registers is a waste of space (besides which it should not compile) as the entry into a interrupt event causes a saving of all the key registers (typically on the stack of the currently running process) All the key registers (like the PC and Status registers) are restored upon exit from the interrupt.

The compiler will cause any general purpose registers changed in the interrupt function to be saved/restored.) If you are working at such a low level, then you should know exactly where the interrupt vectors are located, you should have a code segment that overlays the interrupt vectors and another code segment that mirrors the interrupt vectors. Then, you copy the current set of interrupt vectors to the mirror and then replace the desired individual vector with a pointer to the interrupt function you wrote. At the end of your code, you need to copy the vector back into the original vector area. It could be that functions you are having trouble with do those operations for you.

this, from a very old post, from a c.comp news group may be helpful:

You are mixing languages. In Borland C an "interrupt" has type

void (interrupt*)()

while in Borland C++ it has type

void (interrupt*)(...)

This affects the parameter type of setvect and the return type of getvect which change in the same way according to the language used. You obviously compiled your program as a C++ program and not as a C program because according to the compiler's message 'oldvec' is

declared as a "C interrupt" and getvect returns a "C++ interrupt".

Answer 2

the format for using get/set vect() in C, which look nothing like your C++ example is:

tick_isr_old = getvect(0x08);

setvect(0x08, (void interrupt (*)(void)) tick_isr);

Answer 3

As mentioned already, the functions getvect() and setvect() are only available with Borland/Turbo C++. The functions _dos_getvect() and _dos_setvect() are almost identical and offer better portability across compilers (Borland/Turbo C++, MS Visual C++ 1.x, Open Watcom C++). They should be defined in <dos.h>.

Here is an example of their use (prints an '@' every second):

/*** Includes ***/
#include <stdint.h>  // int*_t, uint*_t 
#include <stdbool.h> // bool, true, false 
#include <dos.h>     // _chain_intr(), _dos_getvect() , _dos_setvect()
#include <stdio.h>   // putchar()


/*** Definitions ***/
#define TICKS_PER_SEC   18ul
#define VECT_TIMER      0x1C

/*** Global Variables ***/
bool timer_hooked = false;
bool timer_1sec_elapsed = false;
uint32_t ticks = 0;
void (interrupt far * OrigTimerH)( );   // vector to original 0x1C handler


/*** Functions ***/
static void interrupt far TimerH( void ) {
   ticks++;
   if ( ticks % TICKS_PER_SEC == 0 ) {
      timer_1sec_elapsed = true;
   }
   _chain_intr( OrigTimerH ); // handler callback
}

void TimerStart( void ) {
   __asm { cli }              // critical section; halt interrupts
   OrigTimerH = _dos_getvect( VECT_TIMER ); // save original vector
   _dos_setvect( VECT_TIMER, TimerH );      // put our handler in the vector
   timer_hooked = true;       // remember that we're hooked if we wanted to unhook
   __asm { sti }              // resume interrupts
}

int main( void ) {
   TimerStart();

   while ( true ) {
      if ( timer_1sec_elapsed ) {
            timer_1sec_elapsed = false;
            putchar('@');
      }
   }
}