C 和 C++ 中的指针简介

// 通用语法
datatype *var_name; 
// 一个示例指针“ptr”，它持有
// 一个整数变量的地址或持有
// 一个内存的地址，其值可以
// 通过“ptr”作为整数值访问
int *ptr; 

// The output of this program can be different
// in different runs. Note that the program
// prints address of a variable and a variable
// can be assigned different address in different
// runs.
#include <stdio.h>

int main()
{
int x;

// Prints address of x
printf("%p", &x);

return 0;
}

// C program to demonstrate declaration of
// pointer variables.
#include <stdio.h>
int main()
{
int x = 10;

// 1) Since there is * in declaration, ptr
// becomes a pointer variable (a variable
// that stores address of another variable)
// 2) Since there is int before *, ptr is
// pointer to an integer type variable
int *ptr;

// & operator before x is used to get address
// of x. The address of x is assigned to ptr.
ptr = &x;

return 0;
}

// C program to demonstrate use of * for pointers in C
#include <stdio.h>

int main()
{
// A normal integer variable
int Var = 10;

// A pointer variable that holds address of var.
int *ptr = &Var;

// This line prints value at address stored in ptr.
// Value stored is value of variable "var"
printf("Value of Var = %dn", *ptr);

// The output of this line may be different in different
// runs even on same machine.
printf("Address of Var = %pn", ptr);

// We can also use ptr as lvalue (Left hand
// side of assignment)
*ptr = 20; // Value at address is now 20

// This prints 20
printf("After doing *ptr = 20, *ptr is %dn", *ptr);

return 0;
}

// C++ program to illustrate Pointer Arithmetic
// in C/C++
#include <bits/stdc++.h>

// Driver program
int main()
{
// Declare an array
int v[3] = {10, 100, 200};

// Declare pointer variable
int *ptr;

// Assign the address of v[0] to ptr
ptr = v;

for (int i = 0; i < 3; i++)
{
printf("Value of *ptr = %dn", *ptr);
printf("Value of ptr = %pnn", ptr);

// Increment pointer ptr by 1
ptr++;
}
}

// C++ program to illustrate Array Name as Pointers in C++
#include <bits/stdc++.h>
using namespace std;

void geeks()
{
// Declare an array
int val[3] = { 5, 10, 15};

// Declare pointer variable
int *ptr;

// Assign address of val[0] to ptr.
// We can use ptr=&val[0];(both are same)
ptr = val ;
cout << "Elements of the array are: ";
cout << ptr[0] << " " << ptr[1] << " " << ptr[2];

return;
}

// Driver program
int main()
{
geeks();
return 0;
}

int nums[2][3] = { {16, 18, 20}, {25, 26, 27} };