在原始 USB C++ 中写入文件

Question

this is my code:

int main(int argc, CHAR* argv[]) {

using namespace std;
PVOID data[1024];
DWORD dwBytesRead = 0;
DWORD dwBytesWrite = 512;

HANDLE hFile = CreateFile(L"\\\\.\\E:", GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, 0, OPEN_EXISTING, 0, 0);//open usb 
if (hFile == INVALID_HANDLE_VALUE) {
    printf("Error %x", GetLastError());
    return 1;
}
printf ("created usb hendle\n");
LARGE_INTEGER a = { 50688 };
SetFilePointerEx(hFile, a,NULL,0); //set the pointer to c600 
printf("got usb pointer set\n");
PVOID ToBe = ":) hello this is our file -> ";
if (WriteFile(hFile,ToBe,512 ,&dwBytesWrite,    NULL) == 0)
{
    printf("writeFile error: %x", GetLastError());
    CloseHandle(hFile);
    return 1;
}
printf("write the first string in isb\n");

HANDLE aFile = CreateFile(L"C:\\Users\\h7080y_dxlq\\Downloads\\Video\\88250.mp4", GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, 0, OPEN_EXISTING, 0, 0); //open the file handle

printf("created mp4 hendle\n");
if (aFile == INVALID_HANDLE_VALUE) {
    printf("Error %x", GetLastError());
    return 1;
}
if (ReadFile(aFile, &data, 512, &dwBytesRead, NULL) == 0) {
    printf("ReadFile error: %x", GetLastError());
    return 1;
}
DWORD dwPos;
printf("checked for read errors in mp4 passed o.k.\n");
while (ReadFile(aFile, data,512, &dwBytesRead, NULL) && dwBytesRead > 0) //read file
{
    dwPos = SetFilePointerEx(hFile, a, NULL, 0); 
    LockFile(hFile, dwPos, 0, dwBytesRead, 0);
    WriteFile(hFile, data, 512, &dwBytesWrite, NULL); // write 512 bit chunk at the time to usb 
    UnlockFile(hFile, dwPos, 0, dwBytesRead, 0);
    a = { 50688+512 }; // promot 
}
printf("write all mp4 to the usb directtly\n");

ToBe = "<- this is the end of file , see you soon :)";
if (WriteFile(hFile, ToBe, 512, &dwBytesWrite, NULL) == 0)
{
    printf("writeFile error: %x", GetLastError());
    CloseHandle(hFile);
    return 1;
}

printf("after end massage \n");



CloseHandle(hFile);
system("pause");
return 0;
}

I try to take a file (mp4 in this case) , and read it chunk by chunk (512 bit at the time) , take the chunk and write it to usb and so on till end of file .

Now, the problem is:

A the loop never ends.

B that it don't write the file to the USB, it looks like its write on the same spot again and again...

How can I fix it?

Answer 1

LARGE_INTEGER a = { 50688 };
while (ReadFile(aFile, data,512, &dwBytesRead, NULL) && dwBytesRead > 0) 
{
    dwPos = SetFilePointerEx(hFile, a, NULL, 0); 
    LockFile(hFile, dwPos, 0, dwBytesRead, 0);
    WriteFile(hFile, data, 512, &dwBytesWrite, NULL);
    UnlockFile(hFile, dwPos, 0, dwBytesRead, 0);
    a = { 50688+512 };
}

The first time round the loop you set the file pointer to 50688 and write there. Each subsequent time round the loop you set the file pointer to 50688+512 and write there.

It looks like it writes to the same spot again and again.

Yes indeed. That's exactly what your code specifies. Your should set the file pointer on aFile outside the loop, and let it advance naturally as the file is written. Something like this:

dwPos = 50688;
LARGE_INTEGER a = { dwPos };
if (!SetFilePointerEx(hFile, a, NULL, 0))
{
    // handle error
}
while (ReadFile(aFile, data, 512, &dwBytesRead, NULL) && dwBytesRead > 0) 
{
    LockFile(hFile, dwPos, 0, dwBytesRead, 0);
    WriteFile(hFile, data, 512, &dwBytesWrite, NULL);
    UnlockFile(hFile, dwPos, 0, dwBytesRead, 0);
    dwPos += 512;
}

Note that your calls to LockFile , and the use of a DWORD for dwPos , means that you cannot write a file larger than 4GB.

It is also far from clear to me that the calls to LockFile are needed. Since your original code got the handling of dwPos wrong, it's clear that you weren't locking the parts of the file you intended to. It is my belief that you should simply remove them. In which case the code will become:

LARGE_INTEGER a = { 50688 };
if (!SetFilePointerEx(hFile, a, NULL, 0))
{
    // handle error
}
while (ReadFile(aFile, data, 512, &dwBytesRead, NULL) && dwBytesRead > 0) 
{
    if (!WriteFile(hFile, data, 512, &dwBytesWrite, NULL))
    {
        // handle error
    }
}

You have also omitted large amounts of error checking in this code. I would not be surprised to find that there are a number of other problems with it. I don't particularly want to try to find every single error in your code, and hope that what I have written is enough to help you on your way.