串口之ReadFile、WriteFile函数详解
会设置GetLastError。如启动的是一次异步读操作，则函数会返回零值，并将ERROR_IO_PENDING设置成GetLastError的结果。如结果不是零值，但读入的字节数小于nNumberOfBytesToRead参数指定的值，表明早已抵达了文件的结尾。
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WriteFile
The WriteFile function writes data to a file and is designed for both synchronous and asynchronous operation. The function starts writing data to the file at the position indicated by the file pointer. After the write operation has been completed, the file pointer is adjusted by the number of bytes actually written, except when the file is opened with FILE_FLAG_OVERLAPPED. If the file handle was created for overlapped input and output (I/O), the application must adjust the position of the file pointer after the write operation is finished.
This function is designed for both synchronous and asynchronous operation. TheWriteFileEx function is designed solely for asynchronous operation. It lets an application perform other processing during a file write operation.
BOOL WriteFile( HANDLE hFile, // handle to file LPCVOID lpBuffer, // data buffer DWORD nNumberOfBytesToWrite, // number of bytes to write LPDWORD lpNumberOfBytesWritten, // number of bytes written LPOVERLAPPED lpOverlapped // overlapped buffer );
Parameters
- hFile
-
[in] Handle to the file to be written to. The file handle must have been created with GENERIC_WRITE access to the file.
Windows NT/2000/XP: For asynchronous write operations, hFile can be any handle opened with the FILE_FLAG_OVERLAPPED flag by theCreateFile function, or a socket handle returned by thesocket or accept function.
Windows 95/98/Me: For asynchronous write operations, hFile can be a communications resource opened with the FILE_FLAG_OVERLAPPED flag byCreateFile, or a socket handle returned by socket oraccept. You cannot perform asynchronous write operations on mailslots, named pipes, or disk files.
- lpBuffer
- [in] Pointer to the buffer containing the data to be written to the file.
- nNumberOfBytesToWrite
-
[in] Specifies the number of bytes to write to the file.
A value of zero specifies a null write operation. The behavior of a null write operation depends on the underlying file system. To truncate or extend a file, use theSetEndOfFile function.
Named pipe write operations across a network are limited to 65,535 bytes.
- lpNumberOfBytesWritten
-
[out] Pointer to the variable that receives the number of bytes written.
WriteFile sets this value to zero before doing any work or error checking.
Windows NT/2000/XP: If lpOverlapped is NULL, lpNumberOfBytesWritten cannot be NULL. IflpOverlapped is not NULL, lpNumberOfBytesWritten can be NULL. If this is an overlapped write operation, you can get the number of bytes written by callingGetOverlappedResult. If hFile is associated with an I/O completion port, you can get the number of bytes written by callingGetQueuedCompletionStatus.
If I/O completion ports are used and you are using a callback routine to free the memory allocated to theOVERLAPPED structure pointed to by the lpOverlapped parameter, specify NULL as the value of this parameter to avoid a memory corruption problem during the deallocation. This memory corruption problem will cause an invalid number of bytes to be returned in this parameter.
Windows 95/98/Me: This parameter cannot be NULL.
- lpOverlapped
[in] Pointer to an OVERLAPPED structure. This structure is required ifhFile was opened with FILE_FLAG_OVERLAPPED.
应用实例：
#include
#include
#include
#define STRICT
#define WIN32_LEAN_AND_MEAN
#include
void system_error(char *name) {
char *ptr = NULL;
FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM,
0,
GetLastError(),
0,
(char *)&ptr,
1024,
NULL);
fprintf(stderr, "\nError %s: %s\n", name, ptr);
LocalFree(ptr);
}
int main(int argc, char **argv) {
int ch;
char buffer[1];
HANDLE file;
COMMTIMEOUTS timeouts;
DWORD read, written;
DCB port;
HANDLE keyboard = GetStdHandle(STD_INPUT_HANDLE);
HANDLE screen = GetStdHandle(STD_OUTPUT_HANDLE);
DWORD mode;
char port_name[128] = "\\\\.\\COM3";
char init[] = ""; // e.g., "ATZ" to completely reset a modem.
if ( argc > 2 )
sprintf(port_name, "\\\\.\\COM%c", argv[1][0]);
file = CreateFile(port_name,
GENERIC_READ | GENERIC_WRITE,
0,
NULL,
OPEN_EXISTING,
0,
NULL);
if ( INVALID_HANDLE_VALUE == file) {
system_error("opening file");
return 1;
}
memset(&port, 0, sizeof(port));
port.DCBlength = sizeof(port);
if ( !GetCommState(file, &port))
system_error("getting comm state");
if (!BuildCommDCB("baud=19200 parity=n data=8 stop=1", &port))
system_error("building comm DCB");
if (!SetCommState(file, &port))
system_error("adjusting port settings");
timeouts.ReadIntervalTimeout = 1;
timeouts.ReadTotalTimeoutMultiplier = 1;
timeouts.ReadTotalTimeoutConstant = 1;
timeouts.WriteTotalTimeoutMultiplier = 1;
timeouts.WriteTotalTimeoutConstant = 1;
if (!SetCommTimeouts(file, &timeouts))
system_error("setting port time-outs.");
if (!GetConsoleMode(keyboard, &mode))
system_error("getting keyboard mode");
mode &= ~ ENABLE_PROCESSED_INPUT;
if (!SetConsoleMode(keyboard, mode))
system_error("setting keyboard mode");
if (!EscapeCommFunction(file, CLRDTR))
system_error("clearing DTR");
Sleep(200);
if (!EscapeCommFunction(file, SETDTR))
system_error("setting DTR");
if ( !WriteFile(file, init, sizeof(init), &written, NULL))
system_error("writing data to port");
if (written != sizeof(init))
system_error("not all data written to port");
do {
// check for data on port and display it on screen.
ReadFile(file, buffer, sizeof(buffer), &read, NULL);
if ( read )
WriteFile(screen, buffer, read, &written, NULL);
// check for keypress, and write any out the port.
if ( kbhit() ) {
ch = getch();
WriteFile(file, &ch, 1, &written, NULL);
}
} while ( ch != 127);
.
CloseHandle(keyboard);
CloseHandle(file);
return 0;
}