C miscellaneous shallow copy and deep copy

Catalog

Knowledge point 1【 Introduction of knowledge points 】

  Knowledge point 2【 Deep copy 】

   Knowledge point 3【 summary 】

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Knowledge point 1【 Introduction of knowledge points 】

1、 When there are pointer member variables in the structure , When copying structural variables , There is a difference between shallow copy and deep copy .

namely ： In light copy , After copying, the pointer member variable in the two structure variables points to The same Address

        Deep copy , After copying, the pointer member variable in the two structure variables points to Different Address

typedef struct
{
	int num;
	char *name;// Pointer variable as   Member of a structure 
}DATA;
void test01()
{
	DATA data={100,"hehehehaha"};
	printf("%d\n",sizeof(DATA));//8 byte 

	printf("num = %d\n",data.num);
	// Pointer variable as a member of the structure   Save the address of the space 
	printf("name = %s\n",data.name);
}

2、 Pointer to the variable As a member of a structure Before operation There must be legal space

void test02()
{
	DATA data;
	printf("%d\n",sizeof(DATA));

	printf("num = %d\n",data.num);
	// Pointer to the variable   As a member of a structure   Before operation   There must be legal space 
	//data.name = "hehe";
	// to name  Apply in advance   A piece of   Heap space 
	data.name = (char *)calloc(1,10);
	strcpy(data.name,"hahaha");
	printf("name = %s\n",data.name);

	// If name Point to heap space   Be sure to release 
	if(data.name != NULL)
	{
		free(data.name);
		data.name = NULL;
	}
}

Schematic analysis ：

 3、 Pointer to the variable As a member of a structure Assignment between structural variables Easily lead to “ Shallow copy ” happen

void test03()
{
	DATA data1;
	DATA data2;

	data1.num = 100;
	data1.name = (char *)calloc(1,10);
	strcpy(data1.name,"my data");
	printf("data1:num = %d, name = %s\n",data1.num, data1.name);

	// Pointer to the variable   As a member of a structure   Assignment between structural variables   Easily lead to “ Shallow copy ” happen 
	data2 = data1;//“ Shallow copy ”
	printf("data2: num = %d, name = %s\n",data2.num, data2.name);

	if(data1.name != NULL)
	{
		free(data1.name);
		data1.name = NULL;
	}
	
	if(data2.name != NULL)
	{
		free(data2.name);
		data2.name = NULL;
	}
}

Running results There was a paragraph error

  Knowledge point 2【 Deep copy 】

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct
{
	int num;
	char *name;
}DATA;
void test01()
{
	DATA data1;
	DATA data2;

	data1.num = 100;
	data1.name = (char *)calloc(1,12);
	strcpy(data1.name, "my data");

	data2.num = data1.num;
	// Is the structure variable   apply   Independent space 
	data2.name = (char *)calloc(1,12);
	strcpy(data2.name, data1.name);

	printf("data1:num = %d, name=%s\n", data1.num, data1.name);
	printf("data2:num = %d, name=%s\n", data2.num, data2.name);

	if(data1.name != NULL)
	{
		free(data1.name);
		data1.name = NULL;
	}

	if(data2.name != NULL)
	{
		free(data2.name);
		data2.name = NULL;
	}


}
int main(int argc,char *argv[])
{
	test01();
	return 0;
}

Running results ：

   Knowledge point 3【 summary 】

The premise is pointer variables As Member of a structure

Shallow copy ： Two structural variables Medium Pointer members Point to Same stack space .

Deep copy ： Two structural variables Medium Pointer members Point to Respective heap space .