vc中使用内存映射加快拷贝4g 大文件

内存映射是一种将文件或其他资源映射到内存中的技术，它可以使得对资源的访问变得更加高效。在 Windows 中，内存映射可以通过 CreateFileMapping 和 MapViewOfFile 函数实现。

下面给出一个使用内存映射加快拷贝4G大文件的示例代码：

#include <Windows.h>
#include <iostream>
#include <string>

using namespace std;

int main()
{
    HANDLE hFile = CreateFile("largefile.bin", GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hFile == INVALID_HANDLE_VALUE) {
        cout << "Failed to open file" << endl;
        return 1;
    }

    HANDLE hMapping = CreateFileMapping(hFile, NULL, PAGE_READONLY, 0, 0, NULL);
    if (hMapping == NULL) {
        cout << "Failed to create file mapping" << endl;
        CloseHandle(hFile);
        return 1;
    }

    LPVOID pView = MapViewOfFile(hMapping, FILE_MAP_READ, 0, 0, 0);
    if (pView == NULL) {
        cout << "Failed to map file view" << endl;
        CloseHandle(hMapping);
        CloseHandle(hFile);
        return 1;
    }

    HANDLE hOutFile = CreateFile("largefile_copy.bin", GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hOutFile == INVALID_HANDLE_VALUE) {
        cout << "Failed to create output file" << endl;
        UnmapViewOfFile(pView);
        CloseHandle(hMapping);
        CloseHandle(hFile);
        return 1;
    }

    DWORD fileSizeLow = GetFileSize(hFile, NULL);
    DWORD fileSizeHigh = 0;
    DWORD fileSize = (fileSizeHigh << 32) | fileSizeLow;

    DWORD bytesWritten = 0;
    if (!WriteFile(hOutFile, pView, fileSize, &bytesWritten, NULL)) {
        cout << "Failed to write output file" << endl;
        CloseHandle(hOutFile);
        UnmapViewOfFile(pView);
        CloseHandle(hMapping);
        CloseHandle(hFile);
        return 1;
    }

    cout << "File copied successfully" << endl;

    CloseHandle(hOutFile);
    UnmapViewOfFile(pView);
    CloseHandle(hMapping);
    CloseHandle(hFile);

    return 0;
}

该程序通过内存映射技术将 `largefile.bin` 文件映射到内存中，然后将映射的内存直接写入到 `largefile_copy.bin` 文件中，从而实现快速拷贝4G大文件的功能。需要注意的是，该程序只适用于4G以下的文件，对于更大的文件需要进行分块处理。