c语言编写仪表的dll文件

要编写一个 C 语言的仪表 DLL 文件，可以按照以下步骤进行：

1. 找到你要连接的仪表的 API 文档，了解其通信协议和命令格式；
2. 打开 Visual Studio （或其他 C 语言的集成开发环境）；
3. 创建一个新的 DLL 项目；
4. 编写 C 语言代码，实现仪表的连接、通信和数据解析等功能，并将其编译为 DLL 文件；
5. 在应用程序中添加对 DLL 文件的引用，并调用 DLL 文件中的函数。

下面是一个简单的 C 语言仪表 DLL 文件的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>

#define BUFFER_SIZE 1024

typedef struct {
    HANDLE hComm;
    char szPort[16];
    int nBaudRate;
    int nDataBits;
    int nStopBits;
    int nParity;
} COM_HANDLE;

__declspec(dllexport) COM_HANDLE* OpenCOM(const char* szPort, int nBaudRate, int nDataBits, int nStopBits, int nParity)
{
    COM_HANDLE* pHandle = (COM_HANDLE*)malloc(sizeof(COM_HANDLE));
    pHandle->hComm = CreateFile(szPort, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
    if (pHandle->hComm == INVALID_HANDLE_VALUE) {
        free(pHandle);
        return NULL;
    }

    DCB dcb;
    memset(&dcb, 0, sizeof(dcb));
    dcb.DCBlength = sizeof(dcb);
    GetCommState(pHandle->hComm, &dcb);
    dcb.BaudRate = nBaudRate;
    dcb.ByteSize = nDataBits;
    dcb.StopBits = nStopBits;
    dcb.Parity = nParity;
    SetCommState(pHandle->hComm, &dcb);

    return pHandle;
}

__declspec(dllexport) void CloseCOM(COM_HANDLE* pHandle)
{
    CloseHandle(pHandle->hComm);
    free(pHandle);
}

__declspec(dllexport) int ReadData(COM_HANDLE* pHandle, char* szBuffer, int nBufferSize)
{
    DWORD dwRead = 0;
    if (!ReadFile(pHandle->hComm, szBuffer, nBufferSize, &dwRead, NULL)) {
        return -1;
    }

    return dwRead;
}

__declspec(dllexport) int WriteData(COM_HANDLE* pHandle, const char* szBuffer, int nBufferSize)
{
    DWORD dwWritten = 0;
    if (!WriteFile(pHandle->hComm, szBuffer, nBufferSize, &dwWritten, NULL)) {
        return -1;
    }

    return dwWritten;
}

__declspec(dllexport) int ParseData(const char* szData, int nDataSize, float* pfValue)
{
    if (nDataSize < 4) {
        return -1;
    }

    int nDataLen = szData[0];
    if (nDataLen + 3 > nDataSize) {
        return -1;
    }

    int nValue = 0;
    memcpy(&nValue, szData + 1, sizeof(nValue));
    *pfValue = (float)nValue / 1000.0f;

    return 0;
}

上面的代码实现了连接串口、读写数据和解析数据等功能。在应用程序中可以通过以下方式调用：

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>

typedef struct COM_HANDLE COM_HANDLE;

typedef COM_HANDLE* (*OpenCOM)(const char* szPort, int nBaudRate, int nDataBits, int nStopBits, int nParity);
typedef void (*CloseCOM)(COM_HANDLE* pHandle);
typedef int (*ReadData)(COM_HANDLE* pHandle, char* szBuffer, int nBufferSize);
typedef int (*WriteData)(COM_HANDLE* pHandle, const char* szBuffer, int nBufferSize);
typedef int (*ParseData)(const char* szData, int nDataSize, float* pfValue);

int main()
{
    HMODULE hDll = LoadLibrary("MyDll.dll");

    OpenCOM pfnOpenCOM = (OpenCOM)GetProcAddress(hDll, "OpenCOM");
    CloseCOM pfnCloseCOM = (CloseCOM)GetProcAddress(hDll, "CloseCOM");
    ReadData pfnReadData = (ReadData)GetProcAddress(hDll, "ReadData");
    WriteData pfnWriteData = (WriteData)GetProcAddress(hDll, "WriteData");
    ParseData pfnParseData = (ParseData)GetProcAddress(hDll, "ParseData");

    COM_HANDLE* pHandle = pfnOpenCOM("COM1", 9600, 8, 1, NOPARITY);

    char szBuffer[BUFFER_SIZE];
    int nRead = pfnReadData(pHandle, szBuffer, BUFFER_SIZE);

    float fValue;
    pfnParseData(szBuffer, nRead, &fValue);

    pfnCloseCOM(pHandle);

    FreeLibrary(hDll);

    return 0;
}

这段代码首先加载 DLL 文件，然后通过 GetProcAddress 函数获取 DLL 文件中的各个函数的指针，并调用这些函数来连接串口、读写数据和解析数据等。最后，卸载 DLL 文件。