memmove 对同一个指针不操作

1、memmove 对同一个指针不操作，所以调用memmove之前不用比较两个指针是否相同

 2、使用memmove是比memcpy更安全的

3、https://www.cnblogs.com/luoquan/p/5265273.html

 

void CTestDLLDlg::OnBnClickedButton6()
{
    const int size = 999999;
    char* data = new char[size];
    memset(data, 1, size - 1);

    char* data1 = new char[size];
    memset(data1, 'a', size - 1);

    clock_t begin = clock();
    for (int i = 0; i < size; ++i)
    {
        memmove(data1, data, size);
    }
    clock_t end = clock();

    double duration = 0;
    duration = (double)(end - begin) / CLOCKS_PER_SEC;
    CString str = _T("");
    str.Format(_T("-不同指针复制- %f---\n"), duration);
    OutputDebugString(str);

    clock_t begin1 = clock();
    for (int i = 0; i < size; ++i)
    {
        memmove(data1, data1, size);
    }
    clock_t end1 = clock();

    double duration1 = 0;
    duration1 = (double)(end1 - begin1) / CLOCKS_PER_SEC;
    CString str1 = _T("");
    str1.Format(_T("-同指针复制- %f---\n"), duration1);
    OutputDebugString(str1);


    clock_t begin2 = clock();
    for (int i = 0; i < size; ++i)
    {
    }
    clock_t end2 = clock();

    double duration2 = 0;
    duration2 = (double)(end1 - begin1) / CLOCKS_PER_SEC;
    CString str2 = _T("");
    str2.Format(_T("-空循环- %f---\n"), duration2);
    OutputDebugString(str2);

    delete data;
    data = nullptr;

    delete data1;
    data1 = nullptr;


}

显示结果是：

 

 

-不同指针复制- 49.971000---
-同指针复制- 38.833000---
-空循环- 38.833000---

将memmove换成memcpy，显示

-不同指针复制- 49.782000---
-同指针复制- 38.847000---
-空循环- 38.847000---

 

没觉得memcpy有多快