大侠,怎么直接读取u盘下的文件内容(非系统缓冲中的数据)
请教各位大侠,如何直接读取u盘上的文件内容(非系统缓冲中的数据)？
我的代码如下：
int Handle;
WORD i;
BYTE TmpWBuf[8192];
BYTE TmpRBuf[8192];
int Tmp;
BYTE ch;
if(CreateDirectory("H:\\tmp", NULL))
{
printf("create folder ok\n");
}
if(-1 == (Handle = open("H:\\tmp\\test.txt", O_RDWR | O_CREAT | O_BINARY, 0x0180)))
{
printf("open file error\n");
}
for(i=0; i<512; i++)
{
TmpWBuf[i] = i;
}
write(Handle, TmpWBuf, 8192);
lseek(Handle, 0, SEEK_SET);
read(Handle, TmpRBuf, 2048);//该句并没有直接去读取U盘里的文件内容，而是缓存里的
close(Handle);
怎么做才能直接读取到u盘里的文件呢？请教各位
------解决方案--------------------
试试看，不一定行。
CreateFile
HANDLE CreateFile(
LPCTSTR lpFileName, // pointer to name of the file
DWORD dwDesiredAccess, // access (read-write) mode
DWORD dwShareMode, // share mode
LPSECURITY_ATTRIBUTES lpSecurityAttributes,
// pointer to security attributes
DWORD dwCreationDisposition, // how to create
DWORD dwFlagsAndAttributes, // file attributes
HANDLE hTemplateFile // handle to file with attributes to
// copy
);
Parameters
...
dwFlagsAndAttributes
Specifies the file attributes and flags for the file.
Any combination of the following attributes is acceptable for the dwFlagsAndAttributes parameter, except all other file attributes override FILE_ATTRIBUTE_NORMAL.
Any combination of the following flags is acceptable for the dwFlagsAndAttributes parameter. Flag Meaning
FILE_FLAG_WRITE_THROUGH
Instructs the system to write through any intermediate cache and go directly to disk. The system can still cache write operations, but cannot lazily flush them.
FILE_FLAG_OVERLAPPED
Instructs the system to initialize the object, so that operations that take a significant amount of time to process return ERROR_IO_PENDING. When the operation is finished, the specified event is set to the signaled state.
When you specify FILE_FLAG_OVERLAPPED, the file read and write functions must specify an OVERLAPPED structure. That is, when FILE_FLAG_OVERLAPPED is specified, an application must perform overlapped reading and writing.
When FILE_FLAG_OVERLAPPED is specified, the system does not maintain the file pointer. The file position must be passed as part of the lpOverlapped parameter (pointing to an OVERLAPPED structure) to the file read and write functions.
This flag also enables more than one operation to be performed simultaneously with the handle (a simultaneous read and write operation, for example).
FILE_FLAG_NO_BUFFERING
Instructs the system to open the file with no intermediate buffering or caching. When combined with FILE_FLAG_OVERLAPPED, the flag gives maximum asynchronous performance, because the I/O does not rely on the synchronous operations of the memory manager. However, some I/O operations will take longer, because data is not being held in the cache.
An application must meet certain requirements when working with files opened with FILE_FLAG_NO_BUFFERING:
File access must begin at byte offsets within the file that are integer multiples of the volume's sector size.
File access must be for numbers of bytes that are integer multiples of the volume's sector size. For example, if the sector size is 512 bytes, an application can request reads and writes of 512, 1024, or 2048 bytes, but not of 335, 981, or 7171 bytes.
Buffer addresses for read and write operations must be sector aligned (aligned on addresses in memory that are integer multiples of the volume's sector size).
我的代码如下：
int Handle;
WORD i;
BYTE TmpWBuf[8192];
BYTE TmpRBuf[8192];
int Tmp;
BYTE ch;
if(CreateDirectory("H:\\tmp", NULL))
{
printf("create folder ok\n");
}
if(-1 == (Handle = open("H:\\tmp\\test.txt", O_RDWR | O_CREAT | O_BINARY, 0x0180)))
{
printf("open file error\n");
}
for(i=0; i<512; i++)
{
TmpWBuf[i] = i;
}
write(Handle, TmpWBuf, 8192);
lseek(Handle, 0, SEEK_SET);
read(Handle, TmpRBuf, 2048);//该句并没有直接去读取U盘里的文件内容，而是缓存里的
close(Handle);
怎么做才能直接读取到u盘里的文件呢？请教各位
------解决方案--------------------
试试看，不一定行。
CreateFile
HANDLE CreateFile(
LPCTSTR lpFileName, // pointer to name of the file
DWORD dwDesiredAccess, // access (read-write) mode
DWORD dwShareMode, // share mode
LPSECURITY_ATTRIBUTES lpSecurityAttributes,
// pointer to security attributes
DWORD dwCreationDisposition, // how to create
DWORD dwFlagsAndAttributes, // file attributes
HANDLE hTemplateFile // handle to file with attributes to
// copy
);
Parameters
...
dwFlagsAndAttributes
Specifies the file attributes and flags for the file.
Any combination of the following attributes is acceptable for the dwFlagsAndAttributes parameter, except all other file attributes override FILE_ATTRIBUTE_NORMAL.
Any combination of the following flags is acceptable for the dwFlagsAndAttributes parameter. Flag Meaning
FILE_FLAG_WRITE_THROUGH
Instructs the system to write through any intermediate cache and go directly to disk. The system can still cache write operations, but cannot lazily flush them.
FILE_FLAG_OVERLAPPED
Instructs the system to initialize the object, so that operations that take a significant amount of time to process return ERROR_IO_PENDING. When the operation is finished, the specified event is set to the signaled state.
When you specify FILE_FLAG_OVERLAPPED, the file read and write functions must specify an OVERLAPPED structure. That is, when FILE_FLAG_OVERLAPPED is specified, an application must perform overlapped reading and writing.
When FILE_FLAG_OVERLAPPED is specified, the system does not maintain the file pointer. The file position must be passed as part of the lpOverlapped parameter (pointing to an OVERLAPPED structure) to the file read and write functions.
This flag also enables more than one operation to be performed simultaneously with the handle (a simultaneous read and write operation, for example).
FILE_FLAG_NO_BUFFERING
Instructs the system to open the file with no intermediate buffering or caching. When combined with FILE_FLAG_OVERLAPPED, the flag gives maximum asynchronous performance, because the I/O does not rely on the synchronous operations of the memory manager. However, some I/O operations will take longer, because data is not being held in the cache.
An application must meet certain requirements when working with files opened with FILE_FLAG_NO_BUFFERING:
File access must begin at byte offsets within the file that are integer multiples of the volume's sector size.
File access must be for numbers of bytes that are integer multiples of the volume's sector size. For example, if the sector size is 512 bytes, an application can request reads and writes of 512, 1024, or 2048 bytes, but not of 335, 981, or 7171 bytes.
Buffer addresses for read and write operations must be sector aligned (aligned on addresses in memory that are integer multiples of the volume's sector size).