C++ Memory Management: Memory Allocation Strategies

In C, choosing an appropriate memory allocation strategy is crucial to improving application performance and reliability. Common strategies include: 1. malloc/realloc: classic allocator that manages memory manually; 2. new/delete: C operator, which encapsulates malloc/realloc and automatically releases memory; 3. Smart pointers: avoid memory leaks and wild pointers ; 4. Memory pool: pre-allocate a fixed-size object group; 5. Garbage collection: automatically recycle objects that are no longer used (not commonly used in C).

C Memory Management: Memory Allocation Strategies

In C, memory management is a vital topic. Choosing an appropriate memory allocation strategy can significantly improve the performance and reliability of your application. This tutorial discusses common memory allocation strategies in C and provides practical examples.

Basic principles of memory allocation

In C, memory allocation is done by using the new operator. It requests a block of memory from the heap to store the newly created object. The object's life cycle ends after calling the delete operator, which releases the allocated memory.

Common memory allocation strategies

• malloc/realloc: Classic memory allocator, manually manage memory. It requires explicit freeing of allocated memory, but provides fine-grained control.
• new/delete: C operator, which encapsulates malloc/realloc and provides automatic memory release.
• Smart pointers: Such as std::unique_ptr and std::shared_ptr, manage the memory life cycle of objects to avoid memory leaks and wild pointers.
• Memory pool: Pre-allocate a set of fixed-size objects to avoid allocating and releasing them one by one from the heap.
• Garbage collection: Automatically recycling objects that are no longer used is common in other languages, but not commonly used in C.

Practical case

Consider the following scenario of allocating a large integer array:

int* arr = new int[1000000];  // 分配 100 万个整数

Use the new operator allocated continuously. However, this may lead to memory fragmentation because the memory after an object is released is not always immediately available for reuse. To alleviate this problem, consider using memory pool.

class IntPool {
public:
    IntPool() {
        // 预先分配 10 个内存块，每个块包含 10000 个整数
        for (int i = 0; i < 10; i++) {
            blocks.push_back(new int[10000]);
        }
        current_block = blocks.begin();
    }

    int* allocate(int count) {
        // 从当前内存块分配
        if (*current_block + count <= blocks[0] + 10000) {
            int* ptr = *current_block;
            *current_block += count;
            return ptr;
        } else {
            // 切换到下一个内存块
            current_block++;
            return allocate(count);
        }
    }

    void deallocate(int* ptr, int count) {
        // 释放内存，但保留内存块
        *current_block = ptr;
    }

private:
    std::vector<int*> blocks;
    std::vector<int*>::iterator current_block;
};

int main() {
    IntPool pool;
    int* arr = pool.allocate(1000000);

    // 使用数组

    pool.deallocate(arr, 1000000);
}

By using IntPool, we pre-allocate 10 memory blocks. When an array is allocated, it is allocated from the current block and then switches to the next block if necessary. This approach reduces memory fragmentation and improves application performance.

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