jump table & code pointers

Question

My code looks like this: (n is a number among 0,1,2 and 3, and loc_A/B/C/D each represents a block of code)

int test(int n){
    static void *jt[7]= {&&loc_A, &&loc_B, &&loc_C, &&loc_D};
    goto *jt[n];
  loc_A:
    ......
  loc_B:
    ......
  loc_C:
    ......
  loc_D:
    ......
}

What does "&&loc_A" stands for? Is it the address(or location) of the codes which loc_A represents?

why you want to use jump you can do it without jump.(that is better) I should add that this could help you http://stackoverflow.com/questions/15702297/dynamic-jump-to-label-in-c — Sina R., Jul 07 '13 at 04:06
@imsiso: thank you but actually I was learning the assembly representation of switch statement...and the original c codes are translated to the extended-C form above in order to illustrate the "jump-table". — Allen, Jul 07 '13 at 04:21
@H2CO3: You're right the codes above are actually translated from　a switch statement. — Allen, Jul 07 '13 at 04:22

score 1 · Accepted Answer · answered Jul 07 '13 at 04:01

1

Yes, but it's not standard C. Instead, it's a GNU language extension. Therefore, best avoided.

answered Jul 07 '13 at 04:01

Oliver Charlesworth

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Thanks. Does this "&&" have anything to do with "&" in C? Like the pointer of a pointer or something like that? Or it is created only to stand for a code location. – Allen Jul 07 '13 at 04:17
@Allen: I guess the GNU guys needed to choose a symbol, so they chose one that kind-of alluded to the idea of "address". – Oliver Charlesworth Jul 07 '13 at 04:19

jump table & code pointers

1 Answers1