C++ error: Pointer operation type mismatch, how to modify it?

C is a powerful programming language, but it is easy to make mistakes when writing programs. One of the common errors is "pointer arithmetic type mismatch". This article explains the causes of this error and how to fix it.

Pointer is a very useful data type in C. It allows programmers to directly access data in memory. Pointers can store memory addresses, and pointers can be used to operate on data in memory.

When we use pointers, we must consider the data type pointed by the pointer. If the type pointed to by the pointer is inconsistent with the type of pointer operation, a "pointer operation type mismatch" error will result.

The following is a sample code:

int numbers[] = {1, 2, 3, 4, 5};
char* p = (char*) numbers;

for (int i = 0; i < 5; i++) {
    cout << *(p + i) << endl;
}

In this sample code, we create an integer array, and then convert the first address of the array into a character pointer. Next, we use the pointer plus operator to access elements in the array. Since the address pointed to by the character pointer increases by 1 each time, the result of each output will be uncertain.

When you run the above code, you will get the following error message:

error: invalid conversion from 'int*' to 'char*'

This is because we converted the pointer of the integer array into a character pointer, which is illegal. Since the step size of a character pointer is only 1 byte each time it is incremented by 1, and the step size of an integer array in memory is usually 4 bytes, using a character pointer for pointer addition operations will result in accessing incorrect memory. address, resulting in unpredictable errors.

In order to solve this problem, we need to ensure that the data type pointed to by the pointer is consistent with the type of pointer operation. In the above example code, we need to convert a character pointer to an integer pointer.

The following is the modified code:

int numbers[] = {1, 2, 3, 4, 5};
int* p = numbers;

for (int i = 0; i < 5; i++) {
    cout << *(p + i) << endl;
}

In this modified code, we changed the data type of the pointer from character to integer, and pointed the pointer to the integer array. Therefore, we can now access elements in the array using the pointer plus operator, and each element in the array can be output correctly.

In short, when we write a C program, we must ensure that the data type pointed to by the pointer is consistent with the type of pointer operation. This can avoid "pointer arithmetic type mismatch" errors and ensure the correctness of the program.

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