How to solve C++ runtime error: 'access violation'?

How to solve C runtime error: 'access violation'?

In C programming, runtime errors are one of the challenges we often face. One of the common errors is 'access violation', which usually occurs when trying to access an illegal memory location. This article describes some common causes and solutions, and provides corresponding code examples.

1. Null pointer access

Null pointer access is one of the most common causes of 'access violation' errors. This error occurs when we try to access the memory pointed to by a null pointer.

Here is a sample code:

int* ptr = nullptr;
*ptr = 10; // 此处会发生'access violation'错误

Solution:
Before accessing the pointer, we should check whether it is null. This can be achieved by using conditional statements or assertions.

int* ptr = nullptr;
if (ptr != nullptr) {
    *ptr = 10; // 在访问指针之前先进行空指针检查
}

Or use assertions to perform null pointer checks

int* ptr = nullptr;
assert(ptr != nullptr); // 运行时将会中断执行
*ptr = 10;

2. Array out-of-bounds access

Another common cause of 'access violation' errors is Array out of bounds access. This error occurs when we try to access an index outside the array.

The following is a sample code:

int arr[5];
for (int i = 0; i <= 5; ++i) {
    arr[i] = i; // 此处会发生'access violation'错误
}

Solution:
When accessing the array, we should ensure that the index value is within the valid range of the array.

int arr[5];
for (int i = 0; i < 5; ++i) {
    arr[i] = i; // 索引值在有效范围内
}

3. Object pointer access

Another common mistake is accessing through an object pointer that has been deleted or released.

The following is a sample code:

class MyClass {
public:
    void doSomething() { /* ... */ }
};

MyClass* ptr = new MyClass;
delete ptr;
ptr->doSomething(); // 此处会发生'access violation'错误

Solution:
Before using a pointer, you should ensure that the object it points to exists.

MyClass* ptr = new MyClass;
if (ptr != nullptr) {
    ptr->doSomething(); // 在使用指针之前确认其指向的对象存在
}

4. Accessing freed memory

In C programming, we sometimes manually release dynamically allocated memory areas. However, if we continue to use the pointer to the memory after freeing it, an 'access violation' error will occur.

The following is a sample code:

int* ptr = new int;
delete ptr;
*ptr = 10; // 此处会发生'access violation'错误

Solution:
After releasing the memory, we should ensure that the pointer pointing to the memory is no longer used.

int* ptr = new int;
delete ptr;
ptr = nullptr; // 将指针置为空指针，避免误用

Summary:
The 'access violation' error is one of the common runtime errors in C programming. This article provides some common causes and solutions, along with corresponding code examples. When programming in C, we should carefully check pointer and array access to avoid such errors.

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