c - 宏(C)中的预递增

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Macros and postincrement
（8个答案）
我有个问题要问这个代码会打印什么。我看到答案是5，但我搞不懂为什么，++发生了什么？价值到底会增加到哪里？谢谢您！

        #include <stdio.h>
        #define Max(a,b) ((a>b)?a:b)
        int foo(int num1, int num2)
        {
            return Max(num1, ++num2);
        }
        void main()
        {
            int a = 4, b = 3;
            int res = foo(a, b);
            printf("%d\n",res);
            return 0;
        }

    Edit: So I tried to change the code and see if i get the point.
Now what happens after the replacement is: ((4>4++)?4:5++) so when i enter it to the parameter a it should hold the value 6 but I see that its 5 and again i cant get why. Thanks
    #include <stdio.h>
    #define Max(a,b) ((a>b)?a:b)
    int foo(int num1, int num2)
    {
        int a= Max(num1, num2++);
        return a;
    }
    void main()
    {
        int a = 4, b = 4;
        int res = foo(a, b);
        printf("%d\n",res);
        return 0;
    }

最佳答案

宏替换之后，foo()函数看起来像

int foo(int num1, int num2) {
    return ((num1>++num2)?num1:++num2);
}

现在通过将num1值视为4和num2值视为3来解决下面的问题

     Here num2            Here num2
      become 4             becomes 5
        |                   |
((num1 > ++num2) ?  num1 :  ++num2)
   |
(( 4   >   4 )   ?
       |
    false i.e it will return ++num2 as a output & which in turns return 5

旁注，上面一个是简单的三元运算符，下面是它的工作原理

operand-1 ?  operand-2 : operand-3 ;

首先求解operand-1，如果其结果为true(non-zero)，operand-2将视为输出，否则operand-3。在您提到的代码中，返回foo()，即operand-3。

关于c - 宏(C)中的预递增，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/50762518/