C语言内存管理全解析

内存管理基础概念

C语言的内存管理通过手动分配和释放实现，核心分为栈内存（自动管理）和堆内存（手动管理）。栈内存用于局部变量和函数调用，生命周期随作用域结束自动释放；堆内存通过 malloc、calloc、realloc 和 free 动态管理，需程序员显式控制。

动态内存分配函数

malloc
分配指定字节的未初始化内存块，返回 void* 指针。若失败返回 NULL。

int *arr = (int*)malloc(10 * sizeof(int)); // 分配10个整型空间
if (arr == NULL) { /* 处理分配失败 */ }

calloc
分配并初始化内存为0，参数为元素数量和单个元素大小。

int *arr = (int*)calloc(10, sizeof(int)); // 分配且初始化为0

realloc
调整已分配内存块的大小，可能移动数据到新地址。

arr = (int*)realloc(arr, 20 * sizeof(int)); // 扩展为20个整型

内存释放与常见错误

free
释放动态内存，避免内存泄漏。释放后指针应置为 NULL 防止悬垂指针。

free(arr);
arr = NULL; // 避免野指针

常见错误

内存泄漏：未释放不再使用的内存。
越界访问：读写超出分配范围的内存。
双重释放：重复释放同一指针。
野指针：释放后未置空指针。

内存操作函数

memcpy
复制内存块，不处理重叠区域。

char src[] = "Hello";
char dest[10];
memcpy(dest, src, strlen(src) + 1); // 包括终止符

memmove
安全处理内存重叠的复制。

char str[] = "abcdef";
memmove(str + 2, str, 4); // 结果: "ababab"

memset
初始化内存为指定值。

int arr[5];
memset(arr, 0, 5 * sizeof(int)); // 全部置0

memcmp
比较内存内容，返回差异标志。

int cmp = memcmp(arr1, arr2, sizeof(arr1));

高级技巧与优化

内存池：预分配大块内存减少频繁调用 malloc。
对齐访问：使用 aligned_alloc 或编译器扩展提升性能。
调试工具：Valgrind、AddressSanitizer 检测内存错误。

实战示例：动态数组实现

typedef struct {
    int *data;
    size_t size;
    size_t capacity;
} DynamicArray;

void initArray(DynamicArray *arr, size_t initCapacity) {
    arr->data = (int*)malloc(initCapacity * sizeof(int));
    arr->size = 0;
    arr->capacity = initCapacity;
}

void pushBack(DynamicArray *arr, int value) {
    if (arr->size >= arr->capacity) {
        arr->capacity *= 2;
        arr->data = (int*)realloc(arr->data, arr->capacity * sizeof(int));
    }
    arr->data[arr->size++] = value;
}

void freeArray(DynamicArray *arr) {
    free(arr->data);
    arr->data = NULL;
    arr->size = arr->capacity = 0;
}

通过深入理解内存函数及实践，可编写高效、安全的C程序。

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