How to solve C++ runtime error: 'accessing null pointer'?

How to solve C runtime error: 'accessing null pointer'?

Introduction:
C is a powerful and widely used programming language, but when writing code, we often encounter various errors. One of them is the "accessing null pointer" runtime error, also known as NUll pointer access error. This article will describe how to resolve this error and provide some code examples to help readers understand better.

What is a NUll pointer access error?
The NULL pointer is a pointer to a null address. When we try to access the memory location pointed to by the NULL pointer, a runtime error of "accessing null pointer" will occur. This error often causes the program to crash or produce unpredictable results.

Solution:

1. Check if the pointer is null:
   Always check if the pointer is null before accessing it. You can use conditional statements such as if statements to check the value of a pointer. Here is an example:

int* ptr = nullptr; // NULL指针
if(ptr != nullptr) {
    // 访问指针
    // ...
}

In the above example, we initialized a pointer ptr using nullptr and then used a conditional statement to check if the pointer is null. It is only safe to access a pointer if it is not null.

2. Initialize pointer:
   When declaring a pointer variable, always initialize it to a known legal value rather than leaving it uninitialized. Here is an example:

int* ptr = nullptr; // 初始化为NULL指针

or

int* ptr = new int(10); // 初始化为指向整数的指针

In the above example, we used nullptr to initialize the pointer ptr, or use new The operator dynamically allocates an integer and initializes the pointer ptr to point to it.

3. Avoid dangling pointers:
   A dangling pointer refers to a pointer that still exists after the pointer is released or the object it points to is destroyed. Dangling pointers are a common cause of 'accessing null pointer' errors. Make sure to set the pointer to NULL or nullptr after releasing the pointer or ending the object's lifetime to avoid dangling pointer errors. Here is an example:

int* ptr = new int(10); // 分配内存
// 在使用指针之后释放它
delete ptr;
ptr = nullptr; // 将指针设置为空

In the above example, we have allocated memory for the pointer using new operator and after using the pointer use deleteRelease it. We then set the pointer to NULL to avoid dangling pointers.

4. Use smart pointers:
   The C standard library provides smart pointers that can automatically manage the life cycle of objects and automatically release memory when it is no longer needed. Using smart pointers can greatly reduce the possibility of NUll pointer access errors. Here is an example:

#include <memory>

std::shared_ptr<int> ptr = std::make_shared<int>(10); // 使用shared_ptr智能指针

In the above example, we use the std::make_shared function to create a shared_ptr smart pointer, which will be Automatically free memory when no longer referenced and ensure that NULL pointer access errors do not occur.

Conclusion:
The 'accessing null pointer' error is one of the common errors in C program development. To avoid this error, we should always check if the pointer is null, initialize pointer variables, avoid dangling pointers, and use smart pointers to manage the lifetime of objects. By taking these precautions, we can effectively solve the 'accessing null pointer' error and improve the stability and reliability of the program.

Reference:

1. Cplusplus.com. "Null-pointers"
2. GeeksforGeeks.org. "Null Pointers in C/C "

The above is the method to solve the C runtime error: 'accessing null pointer'. I hope it will be helpful to readers. It is normal to encounter errors in programming. It is important to learn to solve them and further improve your programming skills.

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