C language macro definition (macro parameter creation string, pretreatment adhesive)

        #define CNAME value    perhaps #define CNAME expression, Common definitions of constants are as follows , But the macro definition is much more flexible than expected . It can define macro constants 、 Macro functions , You can also enter data types . However , Macro definitions can also directly convert other types of data into char* String of type , Used as pretreatment adhesive .

1. Basic knowledge of macro definition

        #define It is expanded in the preprocessing stage , as everyone knows C The compilation process of the language requires 4 Stage pretreatment 、 compile 、 assembly 、 Links here are not explained one by one , obviously define It will be launched in the initial stage ,define No type and safety checks . also define Will not be allocated memory space .

2.C Predefined macros in language （ Abstract ）

        __LINE__: Represents the line number of the current source code

        __FILE__: Indicates the name of the current source file

        __DATE__: Indicates the date when the file was compiled

        __TIME__: Indicates when the file was compiled

        __STDC__: The procedure is required to be strictly followed ANSI C The identifier is assigned as 1.

        __func__ || __FUNCTION__: Indicates the name of the currently compiled function .

#include<stdio.h>

void print(void){
        printf("%d\n",__LINE__);
        printf("%s\n",__FILE__);
        printf("%s\n",__DATE__);
        printf("%s\n",__TIME__);
        printf("%s\n",__func__);
        printf("%s\n",__FUNCTION__);
        printf("%d\n",__STDC__);
}

int main(){
        print();
        return 0;
}

Output results ： 

4
temp.c
Dec 16 2021
19:44:30
print
print
1

 3. Macro functions ( Macro with parameters )

        #define MACRO_NAME(ARGLIST) CONTENT 

        //MACRO_NAME Macro function name

        //ARGLIST parameter list , No type is required , At this point, the variable length （...）

        //CONTENT Replacement statement

        Here is a simple example for everyone to understand .

#include<stdio.h>

#define T(type,b) type c = b
#define MAX(a,b) a>b?a:b

int main(){
        T(int,10);
        printf("%d\n",c);
        printf("%d\n",MAX(2,3));
        return 0;
}

Output results ：

10

3

4. Create a string with macro parameters  ：# operation

        use # No. creates a string

        define STR(arg) #arg // You can convert any form of input into a string

#include<stdio.h>
#define STR(arg) #arg
int main(){
        int x=1;
        printf(STR(1234));
        printf(STR(Hello world!));
        printf(STR(x));
        return 0;
}
~

Output results ：

1234

Hello world！

x                            // No 1 Because he will x Directly as characters

5. Pre processor adhesive ： ##

  Adhesion of variables , Very useful ！！！ Go straight to the code .

#include<stdio.h>

#define CON(a) v__##a
#define PRINT(n) printf("v__"#n"=%d\n",CON(n))
int main(){
        int CON(1) = 1;
        int CON(2) = 2;
        int CON(a) = 3;

        printf("%d\n",v__1);
        printf("%d\n",v__2);
        printf("%d\n",CON(a));
        printf("%d\n",v__a);

        PRINT(1);
        PRINT(2);
        PRINT(a);

        return 0;
}

Output results ：

1
2
3
3
v__1=1
v__2=2
v__a=3