function passing pointer

method one:

The main function pointer is initialized, and the sub-function assigns the pointer value

#include <iostream>
using namespace std;

void sonFunc(int *c)
{
     *c = 100;
     printf("The value of the C is :%d\n",*c);
     printf("The address of the C is :0x%x\n",c);
}

int main()
{
      int a = 10;
      int *b;
      printf("The address of the A is : 0x%x\n", &a);
      printf("The address of the B is : 0x%x\n", b);
      /* 指针初始化 */
      b = &a;
      printf("The value of the B is : %d\n", *b);
      printf("The address of the B is : 0x%x\n", b);
      /* 传递int型指针b */
      sonFunc(b);
      printf("The value of the B is : %d\n", *b);

      return 0;
}

Result: The address of pointer b after initialization is consistent with the address passed into the sub-function.

Method 2:

The main function defines an integer variable, passes the address of the integer variable, and the sub-function assigns a value to *(&a);

In the sub-function sonFunb(), the address assignment (locally effective) becomes effective after returning to the main function.

#include <iostream>
using namespace std;


void sonFunc(int *c)
{
     *c = 100;
     printf("The value of the C is :%d\n",*c);
     printf("The address of the C is :0x%x\n",c);
}

void sonFunb(int *b)
{
	int d = 111;
	printf("The address of the B is : 0x%x\n", b);
	printf("The address of the D is :0x%x\n",&d);
	/* 子函数中地址赋值，不改变主函数中变量a的地址 */
	b = &d;
	printf("The address of the B is :0x%x\n",b);
	printf("The value of the B is :%d\n",*b);
}

int main()
{
      int a = 10;
      printf("The address of the A is : 0x%x\n", &a);

      /* 传递int型变量a的地址 */
      sonFunb(&a);
      printf("The address of the A is : 0x%x\n", &a);
      printf("The value of the A is : %d\n", a); 	
      
      /* 传递int型变量a的地址 */
      sonFunc(&a);
      printf("The address of the A is : 0x%x\n", &a);
      printf("The value of the A is : %d\n", a);

      return 0;
}

result:

The problem of passing parameters by function pointers is, in the final analysis, the problem of passing parameters. Some details are reflected in the code given above.