Question

代码：

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <Windows.h>

HANDLE creatFile(void);
long WriteBuffer(HANDLE);
char * GetBuffer(void);

void main(void)
{
HANDLE hFile;
printf("CreateFile: ");
hFile = creatFile();
if(hFile != NULL) 
    {
    WriteBuffer(hFile);
    FlushFileBuffers(hFile);
    }
CloseHandle(hFile);
printf("\n\rDone");
getchar();
}

HANDLE creatFile(void)
{
HANDLE hFile;
LPCWSTR sFileName  = L"\\\\.\\E:";
DWORD dwDesiredAccess =  GENERIC_WRITE;
DWORD fShareMode = FILE_SHARE_WRITE | FILE_SHARE_WRITE;
DWORD fCreationDisposition = OPEN_EXISTING;
DWORD fFlagsAndAttributes = FILE_ATTRIBUTE_NORMAL;

hFile = CreateFile(sFileName, dwDesiredAccess,fShareMode,
    NULL, fCreationDisposition, fFlagsAndAttributes,
    NULL);

if (hFile == INVALID_HANDLE_VALUE)
{
    hFile = NULL;
    printf("INVALID_HANDLE_VALUE: ");

    switch (GetLastError())
                {
    case 5:
        printf("\n\r Administrative Account required to run this program\n\r");
        break;
    case 87:
        printf("\n\r Invalid Parameter in CreateFile Call \n\r");
        break;
    default:

        printf("Error %d\n",GetLastError());
        break;
    }




    return NULL;
}
else
{
    printf("Attached -> %d\n\r",hFile);
    return hFile;
}
}


long WriteBuffer(HANDLE hFile)
{
char *str = GetBuffer(); // x 64 will give us 512 (sector sized buffer) ;
DWORD bytesWritten;
long totalBytesWritten = 0;
long idx = 0;
int len = strlen(str);

for(idx = 0; idx < 100000; idx ++)
{

    if(WriteFile(hFile, str, 512  * sizeof(char), &bytesWritten, NULL))
    {

        totalBytesWritten += bytesWritten;
        printf("Sectors Written : %d\r",idx+1);
    }
    else
    {
        int le = GetLastError();
        printf("Last Error : %d\r",GetLastError());
        break;
    }
}
printf("\n\r");
printf("Bytes Written: %d\n\r", totalBytesWritten);
printf("Handle -> %d\n\r",hFile);
return totalBytesWritten;
}

char * GetBuffer(void)
{
int i = 0, idx = 0;
const char * cstr_init = "ERASED1 ";
char *buffer = (char*)malloc(512);
char word2[512];

for (idx = 0; idx < 512; idx+=8) {
    for (i = 0; i < 8; i++) {
        buffer[idx+i] = cstr_init[i];
        if(strlen(buffer) == 512) 
            break;
    }
}


return buffer;
}

问题：

char * GetBuffer中包含16个字节的无关数据。我修改了WriteFile，它只写了缓冲区实际拥有的512个（而不是528个）字符。
写入16个扇区后 - WriteFile因GetLastError = 5（拒绝访问）而失败

问题：

如何修复WriteFile，使其在16个扇区之后不会失败...
如何修复GetBuffer，使其实际生成512缓冲区而不是528？

备注该应用程序是ANSI C，该程序以管理员身份运行。

Answer 1

我无法通过WriteFile()说出错误，但是，您的字符串操作存在问题。

C字符串以空值终止，也就是说，字符串文字"abc"实际上是一个字符数组，如：{'a','b','c','\0'}所有str...()操作都依赖于此事实。没有信息存储在字符串长度的任何地方，只有事实是它应该以{{1}}结尾。

您的'\0'功能已改进：

GetBuffer()

你得到了char * GetBuffer(void) { int i = 0, idx = 0; const char * cstr_init = "ERASED1 "; char *buffer = malloc(513); // Space for a '\0' for (idx = 0; idx < 512; idx+=8) { for (i = 0; i < 8; i++) { buffer[idx+i] = cstr_init[i]; } } }的奇怪结果，因为它查找strlen()并且只找到一个528字节，读取512字节以外的malloced正在调用未定义的行为，你可能找到了'\ 0'为513字节，或从未找到过。

其他评论，在调用'\0'之后，你永远不会GetBuffer()返回free()，这是一个内存泄漏，因为它已被malloced并在该上下文之外丢失。此外，char *的更好实现将是：

GetBuffer()

Answer 2

INT类型只能是0到65536无符号的2字节数。用LONG（long）替换所有INT类型以开始...不确定您所处的编译器环境 - 因为此更改可能不适用

Answer 3

我无法解决问题2 - 我喜欢的方式。但是，通过Telling WriteFile从528字节的缓冲区中写出512个字节 - 我得到了所需的结果。问题1。

因为磁盘驱动器上有文件系统 - Windows操作系统识别出这一事实并阻止写入完整驱动器。我需要做的就是锁定驱动器，这将使我可以独占访问驱动器。

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <Windows.h>
#include <winioctl.h>

HANDLE creatFile(void);
long WriteBuffer(HANDLE);
char * GetBuffer(void);

void main(void)
    {
HANDLE hFile;
printf("CreateFile: ");
hFile = creatFile();
if(hFile != NULL) 
{
    WriteBuffer(hFile);
    FlushFileBuffers(hFile);
}
CloseHandle(hFile);
printf("\n\rDone");
getchar();
}

HANDLE creatFile(void)
{
HANDLE hFile;
LPCWSTR sFileName  = L"\\\\.\\E:";
DWORD dwDesiredAccess =  GENERIC_WRITE;
DWORD fShareMode = FILE_SHARE_WRITE | FILE_SHARE_WRITE;
DWORD fCreationDisposition = OPEN_EXISTING;
DWORD fFlagsAndAttributes = FILE_ATTRIBUTE_NORMAL;
BOOL bResult = FALSE;                 // results flag
LPDWORD lpBytesReturned = 0;

hFile = CreateFile(sFileName, dwDesiredAccess,fShareMode,
    NULL, fCreationDisposition, fFlagsAndAttributes,
    NULL);

if (hFile == INVALID_HANDLE_VALUE)
{
    hFile = NULL;
    printf("INVALID_HANDLE_VALUE: ");

    switch (GetLastError())
    {
    case 5:
        printf("\n\r Administrative Account required to run this program\n\r");
        break;
    case 87:
        printf("\n\r Invalid Parameter in CreateFile Call \n\r");
        break;
    default:

        printf("Error %d\n",GetLastError());
        break;
    }




return NULL;
}
else
{
    printf("Attached -> %d\n\r",hFile);
// HERE I JUST ADD THE FSCTL_LOCK_VOLUME command to stop Windows preventing me from writing to the drive        
    bResult = DeviceIoControl(hFile,                       // device to be queried
        FSCTL_LOCK_VOLUME,   // dwIoControlCode
        NULL, 0,                       // no input buffer
        NULL, 0,            // output buffer
        lpBytesReturned,                         // # bytes returned
        (LPOVERLAPPED) NULL);          // synchronous I/O

    return hFile;
}
}


long WriteBuffer(HANDLE hFile)
{
char *str = GetBuffer(); // x 64 will give us 512 (sector sized buffer) ;
DWORD bytesWritten;
long totalBytesWritten = 0;
long idx = 0;
int len = strlen(str);

for(idx = 0; idx < 100000; idx ++)
{

    if(WriteFile(hFile, str, 512  * sizeof(char), &bytesWritten, NULL))
    {

        totalBytesWritten += bytesWritten;
        printf("Sectors Written : %d\r",idx+1);
    }
    else
    {
        int le = GetLastError();
        printf("\n\rLast Error : %d\r",GetLastError());
        break;
    }
}
printf("\n\r");
printf("Bytes Written: %d\n\r", totalBytesWritten);
printf("Handle -> %d\n\r",hFile);
return totalBytesWritten;
}

char * GetBuffer(void)
{
const char * cstr_init = "ERASED2 ";
const int cstr_init_len = strlen(cstr_init);
char *buffer = (char*)malloc(513);
int i;
for (i = 0; i < 512; i+=8) {
    memcpy(buffer+i, cstr_init, cstr_init_len);
    // Or strcpy(buffer+1, cstr_init);
    // Or strcat(buffer, cstr_init); // Inefficient because each call runs from buffer[0] to find a '\0' for where to start appending
}
return buffer;
}

因此，为了将来参考，如果您希望直接写入驱动器，首先锁定音量很重要。我知道上面的代码中存在内存泄漏 - 但作为将数据写入驱动器的学习练习，我并不感到困扰。代码将被整理并制作成.dll

如何修复创建缓冲区并将其直接写入磁盘（WriteFile）

3 个答案: