How to solve C++ runtime error: 'accessing deallocated memory'?

How to solve C runtime error: 'accessing deallocated memory'?

[Introduction]
In C programming, various errors are often encountered. One of them is a runtime error when accessing freed memory: 'accessing deallocated memory'. When a program attempts to access memory that has been freed, it will cause unpredictable behavior and program crashes. This article explains the causes of this error and how to avoid and resolve it.

[Cause of error]
Accessing released memory is a common programming error, especially in C. This error usually occurs under the following circumstances:

1. The pointer continues to be accessed after it is released;
2. The pointer is not initialized or points to an invalid memory address;
3. Multiple Free the same piece of memory twice.

[Solution]

1. Ensure that the pointer continues to be accessed after it is not released:
   In C, we need to manually manage memory, including release Dynamically allocated memory. When we use the delete keyword to release memory, we need to ensure that the released pointer is no longer accessed. After freeing the memory, setting the pointer to a null pointer can help us avoid this error.
   Sample code:

   int* ptr = new int;
   delete ptr;
   ptr = nullptr; // 将指针设置为空指针

2. Ensure that the pointer is correctly initialized and points to a valid memory address:
   Before using the pointer, you must ensure that the pointer has been correctly initialized and points to a valid memory address. memory address. For cases where the pointer is uninitialized or points to an invalid memory address, we can avoid this error by dynamically allocating memory.
   Sample code:

   int* ptr = nullptr; //初始化为空指针
   ptr = new int; //分配内存
   *ptr = 10; //指针现在指向有效的内存地址

3. Avoid releasing the same block of memory multiple times:
   In C, releasing the same block of memory multiple times will lead to undefined behavior. In order to avoid this situation, we can check whether the pointer is empty before using the delete keyword.
   Sample code:

   int* ptr = new int;
   delete ptr;
   ptr = nullptr; 
   // 为了避免多次释放同一块内存，我们可以在delete之前添加条件判断
   if (ptr != nullptr) {
    delete ptr;
    ptr = nullptr;
   }

4. Notes when using dynamic arrays:
   When we use dynamic arrays, we need to use the delete[] keyword to release memory instead of A separate delete keyword. This is because the memory allocated by the dynamic array is applied for through new[], not new. Likewise, we also need to ensure that the freed pointer is no longer accessed.
   Sample code:

   int* arr = new int[10];
   delete[] arr;
   arr = nullptr;

[Summary]
Avoiding access to released memory is an important issue in C programming. By properly managing pointers, properly initializing and releasing memory, and avoiding releasing the same memory multiple times, we can effectively prevent and resolve 'accessing deallocated memory' runtime errors. When using dynamically allocated memory, you must operate with caution to avoid memory leaks and invalid pointers, and to improve the stability and reliability of the program.

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