Inline assembly in C: INT command and C variables - c

Question

I'm trying to use assembly in C code using C variables.
My code looks like this:
__asm { INT interruptValue };
Where 'interruptValue' is a variable I get from the user (e.g 15 or 15h).
When I try to compile I get:
Assembler error: 'Invalid instruction
operands'
I don't know what is the correct type for interruptValue . I tried long\int\short\char\char* but none of them worked.

Answer 1

The INT opcode does not allow to specify a variable (register or memory) as an argument. You have to use a constant expression like INT 13h
If your really want to call variable interrupts (and I cannot imagine any case for doing so), use something like a switch statement to decide which interrupt to use.
Something like this:
switch (interruptValue)
{
case 3:
__asm { INT 3 };
break;
case 4:
__asm { INT 4 };
break;
...
}
EDIT:
This is a simple dynamic aproach:
void call_interrupt_vector(unsigned char interruptValue)
{
//the dynamic code to call a specific interrupt vector
unsigned char* assembly = (unsigned char*)malloc(5 * sizeof(unsigned char));
assembly[0] = 0xCC; //INT 3
assembly[1] = 0x90; //NOP
assembly[2] = 0xC2; //RET
assembly[3] = 0x00;
assembly[4] = 0x00;
//if it is not the INT 3 (debug break)
//change the opcode accordingly
if (interruptValue != 3)
{
assembly[0] = 0xCD; //default INT opcode
assembly[1] = interruptValue; //second byte is actual interrupt vector
}
//call the "dynamic" code
__asm
{
call [assembly]
}
free(assembly);
}