Question

Excerpt from winsock2.h:

#define FD_SET(fd, set) do { u_int __i;\
for (__i = 0; __i < ((fd_set *)(set))->fd_count ; __i++) {\
    if (((fd_set *)(set))->fd_array[__i] == (fd)) {\
        break;\
    }\
}\
if (__i == ((fd_set *)(set))->fd_count) {\
    if (((fd_set *)(set))->fd_count < FD_SETSIZE) {\
        ((fd_set *)(set))->fd_array[__i] = (fd);\
        ((fd_set *)(set))->fd_count++;\
    }\
}\
} while(0)

I am passing in fd of type int and set of type fd_set *. It looks like the cause of the warning may originate from the #define for FD_SETSIZE. Another excerpt from the same header:

#ifndef FD_SETSIZE
#define FD_SETSIZE  64
#endif

I redefined FD_SETSIZE to 64U prior to including winsock2.h but this doesn’t seem to fix it.

Answer 1

fd should be of type SOCKET which is u_int.

The relevant line from the macro was:

if (((fd_set *)(set))->fd_array[__i] == (fd)) {

Didn’t occur to me that == is a comparison operator for whatever reason.