C语言visual studio警告：取消对NULL指针“p”的引用
在C语言中，NULL指针是一个特殊的指针，它不指向任何对象或函数。它通常被用于表示一个没有有效值的指针。在C语言标准库中，NULL被定义为(void *)0。void0。
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如图：
main.cpp
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char* argv[])
{
int* p = (int*)malloc(sizeof(int));
*p = 100;
return 0;
}
p怎么就变成NULL指针了？？不是刚malloc给它分配了地址吗？？？
原因，IDE很智能，它察觉到我们用malloc申请空间的时候可能会存在失败的情况，如果失败了，p没有申请到地址，那么*p=100;就是对空指针的引用，是不允许的，
所以，我们只要加个空指针判断，就不会出现警告了：
main.cpp
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char* argv[])
{
int* p = (int*)malloc(sizeof(int));
if (p!=NULL) {
*p = 100;
}
return 0;
}
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文章目录
C语言Visual Studio警告：取消对NULL指针“p”的引用
在使用C语言编程时，开发者经常会遇到一些与指针相关的问题。本文将详细介绍其中之一：取消对NULL指针“p”的引用这个警告。
1. NULL指针概述
在C语言中，NULL指针是一个特殊的指针，它不指向任何对象或函数。它通常被用于表示一个没有有效值的指针。在C语言标准库中，NULL被定义为(void *)0。
#define NULL ((void*)0)
2. NULL指针的引用问题
当试图通过NULL指针访问内存时，程序将会产生错误。这是因为NULL指针并未指向任何有效的内存地址，所以无法通过该指针来读取或写入数据。如果试图这样做，程序可能会崩溃或产生未定义的行为。
以下是一个尝试通过NULL指针访问内存的例子：
int *p = NULL;
*p = 5; // 这将导致程序崩溃
在这个例子中，由于p是一个NULL指针，所以在尝试解引用p（即*p）以写入数据时，程序会崩溃。
3. Visual Studio的警告机制
Visual Studio是一个强大的集成开发环境（IDE），它有一个高级的警告和错误检测系统。当代码可能产生运行时错误时，Visual Studio会显示警告信息。
在上面的例子中，Visual Studio会显示以下警告信息：
警告: 取消对NULL指针“p”的引用
这个警告意味着你正在试图通过NULL指针来访问内存，这可能导致程序崩溃。
4. 如何解决此问题？
要解决这个问题，你需要确保在尝试通过指针访问内存前，该指针已经被初始化并指向了一个有效的内存地址。以下是一个修改后的例子：
int x = 5;
int *p = &x;
*p = 10; // 这是安全的，因为p现在指向了一个有效的内存地址
在这个例子中，p首先被初始化为变量x的地址，然后再通过p来改变x的值。这样是安全的，因为p现在指向了一个有效的内存地址。
5. 参考文献
- Kernighan, B.W., Ritchie, D.M.: The C Programming Language. Prentice Hall (1988)
- Schildt, H.: C: The Complete Reference. McGraw-Hill Education (2000)
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