Stringing of macro parameters and connection of macro parameters in C language

c Macros in language have macros with or without parameters , There are also macros with parameters .
In fact, a macro is equivalent to a string template , Then the preprocessor is at the mark with macro , Expand the macro , Explain the white point , That is, string replacement . But this work happens before compilation , I didn't understand it before , Feeling c How big are macros in language , It's just for you c The code does some string replacement , After replacement , still c Language , Then it begins to compile into instructions such as assembly .
Now let's talk about how to define a macro with parameters , For example, the simplest macro definition

#define MAX(a,b) (a)>(b)?(a):(b)

such , When we meet in code MAX() Sign time , Precompiled processor （ Note that it's not the compiler ） Will automatically replace this template , Then expand and compare the size of two numbers ;
As shown below ：

int getMax(int x,int y) {
    
	return MAX(x, y);
}

On the surface, it seems to reference a macro , In fact, the string is replaced by the preprocessor , And that's what happened ：

int getMax(int x,int y) {
    
	return (x)>(y)?(x):(y);
}

See that? , Macros are just replacement strings , It can't be simpler , I just don't know why other languages don't have the concept of macros .
Understand the concept of macro , that . Let's do two operations on macro parameters , String macro parameters , Connection of macro parameters .
1. String of red parameters , as follows ：

#define STR(a) #a

adopt # This character , You can set the parameters in the macro a Change to string , Examples are as follows

cout << STR(hello everyone!) << endl;

such , You can print out hello everyone！ This string ！
2. Simple connection of macro parameters .

#define JOIN(a,b) a##b

That's easy Of a,b The contents of the two variables do a string splicing operation , The following code will output 1234.

cout << JOIN(12,34) << endl;

Be careful , Just a simple string connection . There is no operation of addition, subtraction, multiplication and division .