C++ Development Notes: Avoid Null Pointer Exceptions in C++ Code

In C development, null pointer exception is a common error, which often occurs when the pointer is not initialized or is continued to be used after being released. Null pointer exceptions not only cause program crashes, but may also cause security vulnerabilities, so special attention is required. This article explains how to avoid null pointer exceptions in C code.

1. Initialize pointer variables

Pointers in C must be initialized before use. If not initialized, the pointer will point to a random memory address, which may cause a Null Pointer Exception. To initialize a pointer, you can point it to a free space or set it to a null pointer. For example:

int* p = nullptr; // Null pointer in C 11
int* q = new int; // Apply for a memory and point q to the memory

2. Check whether the pointer is null

Before using a pointer, you should check whether it is null. If it is null, you should avoid continuing to use it. In C, you can use if statement or ternary operator to check if a pointer is null. For example:

if (p != nullptr) {

// 使用p

}
else {

// 处理空指针异常

}

int a = p ? p : 0; //Ternary operator, if p is not empty, take p, otherwise take 0

3. Use smart pointer

Use smart Pointers can reduce the risk of null pointer exceptions in C code. A smart pointer is a class that encapsulates a pointer, which can automatically manage the life cycle of the pointer and automatically release the pointer when it is no longer needed. C 11 introduced two types of smart pointers: shared_ptr and unique_ptr.

shared_ptr allows multiple pointers to share the same object and will automatically delete it when all pointers no longer refer to the object. unique_ptr only allows one pointer to have ownership of an object, and will automatically delete the object when the pointer expires.

4. Avoid freeing a freed pointer

Freeing a freed pointer will result in undefined behavior. To avoid this, set the pointer to nullptr before releasing it. For example:

delete p;
p = nullptr;

5. Avoid creating pointers to temporary objects on the stack

If using a pointer to The pointer of the temporary object is stored on the stack. When the temporary object is destroyed, the pointer will point to a piece of memory that has been released, which will cause a null pointer exception. To avoid this, you can use the new operator to place the object on the heap and use smart pointers to manage the pointer's lifetime.

Summary

In C development, it is very important to avoid null pointer exceptions. The risk of null pointer exceptions in C code can be effectively reduced by initializing pointer variables, checking whether pointers are null, using smart pointers, avoiding releasing pointers that have been released, and avoiding creating pointers to temporary objects on the stack. When writing C code, be sure to pay attention to the initialization and use of pointers to avoid unnecessary errors and security holes.

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