what is far function pointer in c language and what is syntax of it?

Question

What is syntax of far function pointer and what is use of "far" in below statement in c language given below? Why far is used in his statement ?

int (far *directCall_setBank)(void);

int VBE_getModeInfo(short mode) {
    VBE_ModeInfoBlock modeInfo;  //Temporary holding space for returned VBE info

    REGS r;        //Register structures for passing to 'int86x()'
    SREGS s;       //(SREGS includes the segment registers)

    r.x.ax=0x4F01; //AL = 0x01, "get VBE Mode Info"
    r.x.cx=mode;   //CX = mode to get info for
    r.x.di=FP_OFF(&modeInfo);   //address ES:DI to our ModeInfoBlock structure
    s.es=FP_SEG(&modeInfo);     //so that the VBE driver will fill its values

    int86x(0x10,&r,&r,&s); //call interrupt 0x10 (through a C function call)

    screen_width=modeInfo.resX;    //Store the values returned in
    screen_height=modeInfo.resY;   //'modeInfo'
    directCall_setBank=modeInfo.winFuncPtr; //INCLUDING the pointer to our function
    return((int)r.h.ah); //Return the VBE status in AH
}

far and near are both modifiers used with the older segmented memory model of the Intel 8086 family of 16 bit processors. With the introduction of 32 bit memory addresses and modern compilers they are no longer main stream though there may be niches of use. — Richard Chambers, Nov 07 '14 at 13:52
this looks like old MSDOS code to modify the displayed screen resolution. Doing a bit of archaeology? — Richard Chambers, Nov 07 '14 at 13:57
possible duplicate of [difference between far pointer and near pointer in C](http://stackoverflow.com/questions/1749904/difference-between-far-pointer-and-near-pointer-in-c) — Raymond Chen, Nov 07 '14 at 13:59

score 2 · Answer 1 · answered Nov 07 '14 at 13:50

2

It was used in dos era and very machine specific (memory model). To keep the C independent of specific architecture, C never accepted far keyword in standard language still it is available as extensions with some compilers.

answered Nov 07 '14 at 13:50

Mohit Jain

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If the code he posted is the actual code he's asking about: his argument declaration is `far *derectCall_setBank`. In which case, the argument is a pointer to a type named `far`, defined by either a `class`, `struct`, `union`, `enum` or `typedef`. For the memory model modifiers, the syntax would be `MyType far* directCall_setBank`. (Given the `FP_OFF` and `FP_SEG` later, I suspect that he's just miscopied something, and that your explication is the correct one.) – James Kanze Nov 07 '14 at 13:57
what my question is that in code given below void(far * ptr)(void) is it syntace for function pointer in which ptr is function pointer – Niravsinh Parmar Nov 09 '14 at 18:43
`http://cdecl.ridiculousfish.com/?q=int+%28*directCall_setBank%29%28void%29%3B` means [directCall_setBank is a pointer to function accepting (void) no arguments returning int](http://cdecl.ridiculousfish.com/?q=int+%28*directCall_setBank%29%28void%29%3B). `far int (*directCall_setBank)(void);` declares `directCall_setBank as far pointer to function (void) returning int`. `int (far *directCall_setBank)(void);` is incorrect syntax and hence will cause a compile time error even on extensions that support `far` keyword. – Mohit Jain Nov 10 '14 at 05:18

what is far function pointer in c language and what is syntax of it?

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