Write a "standard" macro min, which inputs two parameters and returns the smaller one

Interview questions ： Write a ” standard " macro MIN , This macro takes two arguments and returns the smaller one

answer ：

This test is designed for the following purposes ：

1) identification #define Basic knowledge of macro application , This is a very important basic knowledge . Because in embedded (inline) Operator becomes standard C Part of the previous , Macros are the only way to easily generate embedded code , For embedded systems , In order to achieve the required performance , Embedding code is often a must .

2) Knowledge of triple conditional operators . This operator exists C The reason in the language is that it enables the compiler to produce a ratio of if-then-else Better code , It's important to understand this usage .

3) Know how to use parentheses to enclose parameters carefully in macros

4) I also use this question to start discussing the side effects of macros , for example ： What happens when you write the following code ？

least = MIN(*p++, b);

Pay attention to the point ： Be sure to add brackets . Many people often forget to include parentheses in macro definitions , Macros are replacement snippets of code ,define Pay attention to edge effects when defining expressions , For example, the following definitions ：

The reason lies in the pretreatment stage , Compiler will a = N/2 Deal with it as a = 2+3/2