memmove 對同一個指針不操做,因此調用memmove以前不用比較兩個指針是否相同spa
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("-不一樣指針複製- %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("-同指針複製- %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("-空循環- %f---\n"), duration2); OutputDebugString(str2); delete data; data = nullptr; delete data1; data1 = nullptr; }
顯示結果是:指針
-不一樣指針複製- 49.971000---
-同指針複製- 38.833000---
-空循環- 38.833000---code
將memmove換成memcpy,顯示orm
-不一樣指針複製- 49.782000---
-同指針複製- 38.847000---
-空循環- 38.847000---blog
沒以爲memcpy有多快io