C和C++中的指针|S1（简介，算术和数组） _C语言

本文概述

C ++
C

指针存储变量的地址或存储位置。

// General syntaxdatatype *var_name; // An example pointer "ptr" that holds// address of an integer variable or holds// address of a memory whose value(s) can// be accessed as integer values through "ptr"int *ptr;

使用指针：

文章图片
要在C中使用指针, 我们必须了解以下两个运算符。
要访问指向变量的地址, 我们使用一元运算符
&
(与号)返回该变量的地址。例如＆x给我们变量x的地址。

// 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; }

还有一个运算符是
一元*
(星号)用于两件事：
声明指针变量：在C / C ++中声明指针变量时, 其名称前必须带有*。

// 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 varaible (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; }

要访问存储在地址中的值, 我们使用一元运算符(*), 该运算符返回位于其操作数指定地址处的变量的值。这也称为
取消引用
.
C ++

// C++ program to demonstrate use of * for pointers in C++ #include < iostream> using namespace std; 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" cout < < "Value of Var = " < < *ptr < < endl; // The output of this line may be different in different // runs even on same machine. cout < < "Address of Var = " < < ptr < < endl; // We can also use ptr as lvalue (Left hand // side of assignment) *ptr = 20; // Value at address is now 20// This prints 20 cout < < "After doing *ptr = 20, *ptr is " < < *ptr < < endl; return 0; }// This code is contributed by // shubhamsingh10

// 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 = %d\n" , *ptr); // The output of this line may be different in different // runs even on same machine. printf ( "Address of Var = %p\n" , 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 %d\n" , *ptr); return 0; }

输出：

Value of Var = 10Address of Var = 0x7fffa057dd4After doing *ptr = 20, *ptr is 20

下面是上述程序的图示：

文章图片
指针表达式和指针算术
可以对指针执行一组有限的算术运算。指针可以是：

递增(++)
递减(—)
可以将整数添加到指针(+或+ =)
可以从指针中减去一个整数(–或-=)

指针算术是没有意义的, 除非在数组上执行。
注意：指针包含地址。添加两个地址是没有意义的, 因为不知道它将指向什么。减去两个地址可让你计算这两个地址之间的偏移量。

// 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 = %d\n" , *ptr); printf ( "Value of ptr = %p\n\n" , ptr); // Increment pointer ptr by 1 ptr++; } }

Output:Value of *ptr = 10Value of ptr = 0x7ffcae30c710Value of *ptr = 100Value of ptr = 0x7ffcae30c714Value of *ptr = 200Value of ptr = 0x7ffcae30c718

文章图片
【C和C++中的指针|S1（简介，算术和数组）】数组名称作为指针
数组名称的行为类似于指针常量。该指针常量的值是第一个元素的地址。
例如, 如果我们有一个名为val的数组, 则
值
和
＆val [0]
可以互换使用。

// 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; }

Output:Elements of the array are: 5 10 15

文章图片
现在, 如果将此ptr作为参数发送给函数, 则可以以类似方式访问数组val。
指针和多维数组
考虑二维数字数组的指针符号。考虑以下声明

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

通常, nums [i] [j]等于*(*(nums + i)+ j)

指针符号	数组符号	值
(数字)	nums [0] [0]	16
(数字+ 1)	nums [0] [1]	18
(数字+ 2)	nums [0] [2]	20
((数字+1))	nums [1] [0]	25
((数字+1)+1)	nums [1] [1]	26
((数字+1)+ 2)	nums [1] [2]	27