C++ 使用 WriteFile/ReadFile 的串行通信
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/6036716/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Serial Comm using WriteFile/ReadFile
提问by lYriCAlsSH
//#include "StdAfx.h"
#include <stdio.h>
#include <windows.h>
#include <winbase.h>
#include <iostream>
#include <tchar.h>
using namespace std;
int main()
{
int com = 'COM2';
string data = "\n 010400 \n";
char output[32];
//unsigned int length = 0;
DCB config = {0};
bool abContinue = true;
DWORD dwBytesWritten;
DWORD dwBytesRead;
int isRead = false;
HANDLE m_hCommPort = ::CreateFile(L"COM2",
GENERIC_READ|GENERIC_WRITE,//access ( read and write)
0, //(share) 0:cannot share the COM port
0, //security (None)
OPEN_EXISTING,// creation : open_existing
0, // we dont want overlapped operation
0// no templates file for COM port...
);
config.DCBlength = sizeof(config);
if((GetCommState(m_hCommPort, &config) == 0))
{
printf("Get configuration port has a problem.");
return FALSE;
}
config.BaudRate = 9600;
config.StopBits = ONESTOPBIT;
config.Parity = PARITY_NONE;
config.ByteSize = DATABITS_8;
config.fDtrControl = 0;
config.fRtsControl = 0;
if (!SetCommState(m_hCommPort, &config))
{
printf( "Failed to Set Comm State Reason: %d\n",GetLastError());
//return E_FAIL;
}
printf("Current Settings\n Baud Rate %d\n Parity %d\n Byte Size %d\n Stop Bits %d", config.BaudRate,
config.Parity, config.ByteSize, config.StopBits);
int isWritten = WriteFile(m_hCommPort, &data,(DWORD) sizeof(data), &dwBytesWritten, NULL);
//memset(output, 0, sizeof(output));
while (abContinue)
{
isRead = ReadFile(m_hCommPort, output, sizeof(output), &dwBytesRead, NULL);
if(!isRead)
{
abContinue = false;
break;
}
}
cin.get();
}
I am having trouble reading from the com port. If I step through the code, it goes into "isRead = ReadFile(m_hCommPort, output, sizeof(output), &dwBytesRead, NULL);" and doesn't come back out.... This is my first try at this with no success.
我在从 com 端口读取时遇到问题。如果我单步执行代码，它会进入“isRead = ReadFile(m_hCommPort, output, sizeof(output), &dwBytesRead, NULL);” 并且不会回来......这是我第一次尝试，但没有成功。
回答by Jerry Coffin
You might try some code something like this after you've opened the file, but before you try to use it:
在打开文件之后，但在尝试使用它之前，您可以尝试一些类似这样的代码：
COMMTIMEOUTS timeouts;
timeouts.ReadIntervalTimeout = 1;
timeouts.ReadTotalTimeoutMultiplier = 1;
timeouts.ReadTotalTimeoutConstant = 1;
timeouts.WriteTotalTimeoutMultiplier = 1;
timeouts.WriteTotalTimeoutConstant = 1;
if (!SetCommTimeouts(m_hCommPort, &timeouts))
// setting timeouts failed.
Edit: perhaps it's easier to start with some code that works, and make it do what you want rather than trying to get your code to work. Here's a simple terminal program. It's minimalist in the extreme, but does work (at least well enough to let me see output from my GPS, for one example). It's a long ways from what anybody (least of all me) would call sophisticated, but should give at least some idea of how to get started.
编辑：也许更容易从一些有效的代码开始，让它做你想做的事，而不是试图让你的代码工作。这是一个简单的终端程序。它是极端的极简主义，但确实有效（例如，至少足以让我看到 GPS 的输出）。这与任何人（至少是我）所说的复杂相距甚远，但至少应该给出一些如何开始的想法。
#include <stdio.h>
#include <conio.h>
#include <string.h>
#define STRICT
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
void system_error(char *name) {
// Retrieve, format, and print out a message from the last error. The
// `name' that's passed should be in the form of a present tense noun
// (phrase) such as "opening file".
//
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]);
// open the comm port.
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;
}
// get the current DCB, and adjust a few bits to our liking.
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");
// set short timeouts on the comm port.
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.");
// set keyboard to raw reading.
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");
// basic terminal loop:
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);
}
// until user hits ctrl-backspace.
} while ( ch != 127);
// close up and go home.
CloseHandle(keyboard);
CloseHandle(file);
return 0;
}
回答by Judge Maygarden
If you do not explicitly set the timeouts, then ReadFile will indefinitely block until data becomes available.
如果您没有明确设置 timeouts，那么 ReadFile 将无限期地阻塞，直到数据可用。
回答by Nei
回答by Neil
I had this problem on a readfile, with the timeouts set. This was driving me crackers so I ended up getting some code from the web which did work and then changing line by line to see where the error was.
我在 readfile 上遇到了这个问题，并设置了超时。这让我很崩溃，所以我最终从网上获取了一些确实有效的代码，然后逐行更改以查看错误所在。
Turns out he readfile was fine. My problem was a WaitCommEvent which was hanging when the port was disconnected as no com event is ever received...
原来他 readfile 很好。我的问题是 WaitCommEvent 当端口断开连接时挂起，因为没有收到 com 事件...
