Explain in detail the differences between real participation formal parameters in C language

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Basic concepts

It is no wonder that we have seen so many concepts about shape participation arguments , Here we will deepen our impression or understanding .
Actual parameters : The so-called argument is the variable parameter of the space actually opened up in memory .
Shape parameter ： It refers to the parameters of the function , It is called formal parameter , The reason is that only when the function is called will the variable be given a value in Stack Open up space in , And will The argument is copied to the formal parameter

Case study 1

Here I'll just go up the pointer , We understand the pointer , Everything and understand , Please look at the following code

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

void  func(char * buffer){
    
    printf("%x\n",buffer);
    if(buffer){
    
        free(buffer);
        buffer=NULL;
    }
    return ;
}   
int main(){
    
    char *buf=NULL;
    printf("%x\n",buf);
    buf =(char *)malloc(100);
    if(buf==NULL){
    
        printf("test_1\n");
    }
    func(buf);
    if(buf==NULL){
    
        printf("test_2");
    }else{
    
        printf("test_3");
    }
    return 0;
}

What is the print result of the final program ？

Case study 2

Please look at the following code

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

void swap(int * a,int *b)
{
    
    int *temp;
    temp = a;
    a=b;
    b=temp;
    printf("%d %d\n",*a,*b);
    return ;
}  
int main(){
    
    int a=6;
    int b=10;
    int *p,*q;
    p=&a;
    q=&b;
    swap(p,q);
    printf("%d %d\n",*p,*q);
    return 0;
}

What is the output of this code ？

answer

Case study 1：

answer ：test_3
The analysis is as follows ：
We applied for results on the heap 100 Bytes of space ,malloc Function will return the address on the heap address of the successful application , So I can't print test_1 Of , Then we call the function func, Go to Release parameter buffer, This space on the heap must have been released . And buffer It's empty , But it's none of our business buf What does it matter , therefore buf Not for NULL, The answer is test_3

Case study 2

answer ：
10 6
6 10
The principle is the same as the case 1, Grasp the relationship between actual parameters and formal parameters, and grasp the content copy OK