c语言指针变量初始化

In this tutorial, we will learn how to declare, initialize and use a pointer. We will also learn what NULL pointer are and where to use them. Let's start!

在本教程中，我们将学习如何声明，初始化和使用指针。 我们还将学习什么是NULL指针以及在哪里使用它们。 开始吧！

C指针变量的声明 (Declaration of C Pointer variable)

General syntax of pointer declaration is,

指针声明的一般语法是

datatype *pointer_name;

Data type of a pointer must be same as the data type of the variable to which the pointer variable is pointing. void type pointer works with all data types, but is not often used.

指针的数据类型必须与指针变量指向的变量的数据类型相同。 void类型指针适用于所有数据类型，但并不经常使用。

Here are a few examples:

这里有一些例子：

int *ip     // pointer to integer variable
float *fp;      // pointer to float variable
double *dp;     // pointer to double variable
char *cp;       // pointer to char variable

C指针变量的初始化 (Initialization of C Pointer variable)

Pointer Initialization is the process of assigning address of a variable to a pointer variable. Pointer variable can only contain address of a variable of the same data type. In C language address operator & is used to determine the address of a variable. The & (immediately preceding a variable name) returns the address of the variable associated with it.

指针初始化是将变量的地址分配给指针变量的过程。 指针变量只能包含相同数据类型的变量的地址。 在C语言中， 地址运算符 &用于确定变量的地址。 & (紧邻变量名)返回与之关联的变量的地址。

#include<stdio.h>
    
void main()
{
    int a = 10;
    int *ptr;       //pointer declaration
    ptr = &a;       //pointer initialization
}

Pointer variable always point to variables of same datatype. Let's have an example to showcase this:

指针变量始终指向相同数据类型的变量。 让我们举一个例子来说明这一点：

#include<stdio.h>

void main()
{
    float a;
    int *ptr;
    ptr = &a;       // ERROR, type mismatch
}

If you are not sure about which variable's address to assign to a pointer variable while declaration, it is recommended to assign a NULL value to your pointer variable. A pointer which is assigned a NULL value is called a NULL pointer.

如果不确定在声明时将哪个变量的地址分配给指针变量，建议将NULL值分配给指针变量。 分配了NULL值的指针称为NULL指针 。

#include <stdio.h>

int main() 
{
    int *ptr = NULL;
    return 0;
}

使用指针或指针取消引用 (Using the pointer or Dereferencing of Pointer)

Once a pointer has been assigned the address of a variable, to access the value of the variable, pointer is dereferenced, using the indirection operator or dereferencing operator *.

一旦为指针分配了变量的地址，即可访问该变量的值，就可以使用间接运算符或反引用运算符 *对该指针进行解 引用 。

#include <stdio.h>

int main()
{
    int a, *p;  // declaring the variable and pointer
    a = 10;
    p = &a;     // initializing the pointer

    printf("%d", *p);    //this will print the value of 'a'

    printf("%d", *&a);   //this will also print the value of 'a'

    printf("%u", &a);    //this will print the address of 'a'

    printf("%u", p);     //this will also print the address of 'a'

    printf("%u", &p);    //this will print the address of 'p'
    
    return 0;
}

使用指针时要记住的要点 (Points to remember while using pointers)

1. While declaring/initializing the pointer variable, * indicates that the variable is a pointer.

   在声明/初始化指针变量时， *表示该变量是指针。

2. The address of any variable is given by preceding the variable name with Ampersand &.

   任何变量的地址都在变量名前加上&来给定。

3. The pointer variable stores the address of a variable. The declaration int *a doesn't mean that a is going to contain an integer value. It means that a is going to contain the address of a variable storing integer value.

   指针变量存储变量的地址。 声明int *a并不意味着a将包含一个整数值。 这意味着a将包含一个存储整数值的变量的地址。

4. To access the value of a certain address stored by a pointer variable, * is used. Here, the * can be read as 'value at'.

   要访问指针变量存储的某个地址的值，请使用* 。 在这里， *可以读作'at的值 。

时间为例！ (Time for an Example!)

Let's take a simple code example,

我们来看一个简单的代码示例，

#include <stdio.h>

int main()
{
    int i = 10;     // normal integer variable storing value 10
    int *a;     // since '*' is used, hence its a pointer variable

    /*
        '&' returns the address of the variable 'i' 
        which is stored in the pointer variable 'a'
    */
    a = &i;

    /* 
        below, address of variable 'i', which is stored 
        by a pointer variable 'a' is displayed
    */
   printf("Address of variable i is %u\n", a);

    /*
        below, '*a' is read as 'value at a' 
        which is 10
    */
   printf("Value at the address, which is stored by pointer variable a is %d\n", *a);

   return 0;
}

Address of variable i is 2686728 (The address may vary) Value at an address, which is stored by pointer variable a is 10

变量i的地址为2686728(地址可能有所不同)，该值由指针变量a存储的地址值为10

翻译自: https://www.studytonight.com/c/declaring-and-initializing-pointer.php

c语言指针变量初始化