#include <windows.h> #include <iostream> #include <time.h> using namespace std; struct Cell { char data[128]; }; const int TOTAL_ROWS = 2500; const int TOTAL_COLS = 2500; int main() { clock_t t; t = clock(); Cell* p = (Cell*)malloc(TOTAL_ROWS * TOTAL_COLS * sizeof(Cell)); if (p) { cout << "ok" << endl; } else { cout << "oops" << endl; } (p + (2 * TOTAL_COLS) + 3)->data[0] = 'A'; t = clock() - t; cout << t << endl; t = clock(); p = (Cell*)VirtualAlloc(NULL, TOTAL_ROWS * TOTAL_COLS * sizeof(Cell), MEM_RESERVE, PAGE_READWRITE); if (p) { cout << "ok" << endl; } else { cout << "oops" << endl; } VirtualAlloc(p + (2 * TOTAL_COLS) + 3, sizeof(Cell), MEM_COMMIT, PAGE_READWRITE); (p + (2 * TOTAL_COLS) + 3)->data[0] = 'A'; t = clock() - t; cout << t << endl; return 0; } 在virtual的基础上进行修改，给对角线(左上到右下那条)上所有Cells中的128个元素都赋值成'A'，并用clock函数测量时间。

下面是对代码的修改和解释：

#include <windows.h>
#include <iostream>
#include <time.h>

using namespace std;

struct Cell {
    char data[128];
};

const int TOTAL_ROWS = 2500;
const int TOTAL_COLS = 2500;

int main() {
    clock_t t;
    t = clock();

    // 使用 malloc 分配内存
    Cell* p = (Cell*)malloc(TOTAL_ROWS * TOTAL_COLS * sizeof(Cell));
    if (p) {
        cout << "ok" << endl;
    } else {
        cout << "oops" << endl;
    }

    // 给对角线上的元素赋值为 'A'
    for (int i = 0; i < TOTAL_ROWS && i < TOTAL_COLS; i++) {
        (p + i * TOTAL_COLS + i)->data[0] = 'A';
    }

    t = clock() - t;
    cout << "malloc: " << t << endl;

    t = clock();

    // 使用 VirtualAlloc 分配内存
    p = (Cell*)VirtualAlloc(NULL, TOTAL_ROWS * TOTAL_COLS * sizeof(Cell),
        MEM_RESERVE, PAGE_READWRITE);
    if (p) {
        cout << "ok" << endl;
    } else {
        cout << "oops" << endl;
    }

    // 分配物理内存
    VirtualAlloc(p, TOTAL_ROWS * TOTAL_COLS * sizeof(Cell), MEM_COMMIT, PAGE_READWRITE);

    // 给对角线上的元素赋值为 'A'
    for (int i = 0; i < TOTAL_ROWS && i < TOTAL_COLS; i++) {
        (p + i * TOTAL_COLS + i)->data[0] = 'A';
    }

    t = clock() - t;
    cout << "VirtualAlloc: " << t << endl;

    return 0;
}

上面的修改中，我们在两个内存分配方式中分别给对角线上的元素赋值为 'A'。同时，我们也修改了输出的内容，分别输出使用 malloc 和 VirtualAlloc 分配内存所需的时间。