二级指针堆内存模型--字符串赋值易错点

内存模型图：

当DEBUG为1时直接修改了堆中的内存指向，造成了内存泄漏，而且在free的时候会free常量区直接报错，最好的办法就是用内存拷贝函数执行字符串赋值操作，避免指针指向常量区，造成程序出现bug。

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

#define DEBUG 0

void assignValueTest(char **myp, int num)
{
	printf("enter Func assignValueTest!\n");
	for (size_t i = 0; i < num; i++)
	{
	#if DEBUG == 0
		printf("赋值之前的myp地址:%p\n", myp[i]);
		myp[i] = "1234";		
		printf("常量区字符串“1234”的地址%p\n", "1234");
		printf("赋值之后的myp地址:%p\n", myp[i]);
		printf("---------------------------------------------------\n");
	#else
		strcpy(myp[i], "1234");
	#endif		
	}				
}

int creatMem(char ***myp, int num)
{
	char **p = NULL;
	p = *myp;
	p = (char **)malloc(sizeof(char*) *num);
	if (p == NULL)
	{
		printf("Func creatMem malloc failure\n");
		return -1;
	}
	for (size_t i = 0; i < num; i++)
	{
		p[i] = (char *)malloc(sizeof(char) *num);
		if(p[i] == NULL)
		{
			printf("Func creatMem malloc failure\n");
			return -2;
		}
	}
	assignValueTest(p, num);
	*myp = p;
	
	return 0;
}

void freeMem(char ***myp, int num)
{
	printf("enter Func freeMem!\n");
	char **p = NULL;
	p = *myp;
	for (int i=0; i < num; i++)
	{
		if (p[i] != NULL)
		{
			free(p[i]);
			p[i] = NULL;
		}
	}
	if (p != NULL)
	{
		free(p);
	}
	*myp = NULL;
	printf("Func freeMem run successfuly\n");
}

void printDate(char **myp, int num)
{
	for (int i = 0; i < num; i++)
	{
		printf("%s\n", myp[i]);
	}	
}

int main()
{
	int num = 5;
	char **p = NULL;
	int ret = 0;
	
	ret = creatMem(&p, num);
	if(ret != 0)
	{
		printf("Func creatMem malloc failure\n");
		return -1;
	}
	printDate(p, num);
	freeMem(&p, num);
	
	return 0;
}

当DEBUG=1时的结果：

[[email protected] heima]$ ./a.out 
enter Func assignValueTest!
赋值之前的myp地址:0x1c96040
常量区字符串“1234”的地址0x400a91
赋值之后的myp地址:0x400a91
---------------------------------------------------
赋值之前的myp地址:0x1c96060
常量区字符串“1234”的地址0x400a91
赋值之后的myp地址:0x400a91
---------------------------------------------------
赋值之前的myp地址:0x1c96080
常量区字符串“1234”的地址0x400a91
赋值之后的myp地址:0x400a91
---------------------------------------------------
赋值之前的myp地址:0x1c960a0
常量区字符串“1234”的地址0x400a91
赋值之后的myp地址:0x400a91
---------------------------------------------------
赋值之前的myp地址:0x1c960c0
常量区字符串“1234”的地址0x400a91
赋值之后的myp地址:0x400a91
---------------------------------------------------
1234
1234
1234
1234
1234
enter Func freeMem!
Segmentation fault (core dumped)
[[email protected] heima]$