CODEWITHSUNDEEP
copenvswitch
Arpit Krishna
Arpit Krishna

Reputation: 1

Having diffculties in understanding in c code

Sorry, but i am having the following difficulty in a c code. what is the 3rd line for:

#define LIST_FOR_EACH_SAFE(ITER, NEXT, MEMBER, LIST)               \
    for (INIT_CONTAINER(ITER, (LIST)->next, MEMBER);               \
         (&(ITER)->MEMBER != (LIST)                                \
          ? INIT_CONTAINER(NEXT, (ITER)->MEMBER.next, MEMBER), 1   \
          : 0);                                                    \
         (ITER) = (NEXT))

The entire code can be found at: https://github.com/openvswitch/ovs/blob/ff261703821658243bba13c80311130d036eeb52/include/openvswitch/list.h

SORRY, but this might take up some time for you to get the entire code.

Upvotes: 0

Views: 73

Answers (1)

Henrik Carlqvist
Henrik Carlqvist

Reputation: 1168

This is not a function but a macro so you won't see what types different variables have in any declaration. However, at the second row you can see (LIST)->next which makes it safe to assume that LIST is a pointer to a struct which contains a member called next.

The third row with &(ITER)->MEMBER != (LIST) compares this pointer that LIST points to with the address of MEMBER which is part of a structure that ITER points to.

At the fourth row INIT_CONTAINER(NEXT, (ITER)->MEMBER.next, MEMBER) is called only if the comparision at row 3 differs. After this call is made 1 is the result which is used to continue the for-loop.

At the fift row you instead get result 0 to end the for-loop if the comparision at row 3 would be equal.

Upvotes: 1

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