我想学网页设计，报考以下哪个专业呢？详细介绍一下。计算机应用技术还是数字媒体技术？

 逗号运算符产生其右操作数的值，而不是左操作数。 
 
 更新：正如@Kninnug在评论中指出的那样， sigemptyset是一个指定返回int的POSIX函数（规范： here ）。 通过使用(*(what) = 0, 0)它保证宏产生一个int即使*(what)是另一种类型而不是int （ sigemptyset参数应该是sigset_t类型）。 
 
 你的宏定义让我想到两件事：如果它有(void *) 0作为右边的操作数，它可以模仿一个返回空指针的函数： 
 
#define sigemptyset(what)   (*(what) = 0, (void *) 0)

int *p = sigemptyset(q);
 
 如果所有其他sig函数都应该返回指针，那么它会很有用。 
 
 我想到的第二件事是通过在需要时使用printf调用更改0来允许调试： 
 
 #define sigemptyset(what)   (*(what) = 0, printf("sigemptyset\n"))
 

The comma operator yields the value of its right operand, not the left operand.
 
UPDATE: as pointed out by @Kninnug in the comments, sigemptyset is a POSIX function specified to return an int (specifications: here). By using (*(what) = 0, 0) it guarantees that the macro yields an int even if *(what) is of another type than int (the sigemptyset argument should be of type sigset_t).
 
 Two things come to my mind with your macro definition: If it had (void *) 0 as the right , operand, it could mimic a function that returns a null pointer:
 
 
#define sigemptyset(what)   (*(what) = 0, (void *) 0)

int *p = sigemptyset(q);
 
It can be useful if all your other sig functions are supposed to return pointers.
 
The second thing that comes to my mind is to allow debugging by changing the 0 with a printf call when needed:
 
 #define sigemptyset(what)   (*(what) = 0, printf("sigemptyset\n"))