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POmake a CVICALLBACK a member function in QT creator
 

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  1. POmake a CVICALLBACK a member function in QT creator
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    <p>I found an NI example on how to use some of the DAQmx functions. It's a simple C-file that contains some of the following:</p> <pre><code>... // This is a declaration/definition I think int32 CVICALLBACK ChangeDetectionCallback(TaskHandle taskHandle, int32 signalID, void *callbackData); ... // Later in the script there is actual function int32 CVICALLBACK ChangeDetectionCallback(TaskHandle taskHandle, int32 signalID, void *callbackData) { ... return 0; } </code></pre> <p>When I tend to use some of the variables or functions that are defined in .h file, the ChangeDetectionCallback function does not recognize them. I tried to define this callback function as a member function in .h file, hoping that now all functions will be accessible. Here's my .h content:</p> <pre><code>#ifndef MAINWINDOW_H #define MAINWINDOW_H #include &lt;QMainWindow&gt; #include "NIDAQmx.h" namespace Ui { class MainWindow; } class MainWindow : public QMainWindow { Q_OBJECT public: explicit MainWindow(QWidget *parent = 0); ~MainWindow(); int32 CVICALLBACK ChangeDetectionCallback(TaskHandle taskHandle, int32 signalID, void *callbackData); private: Ui::MainWindow *ui; void mainLoop(); }; #endif // MAINWINDOW_H </code></pre> <p>and here's my .c content:</p> <pre><code>#include "mainwindow.h" #include "ui_mainwindow.h" #include "NIDAQmx.h" #include &lt;stdio.h&gt; #include &lt;string.h&gt; #include &lt;time.h&gt; #define DAQmxErrChk(functionCall) if( DAQmxFailed(error=(functionCall)) ) goto Error; else MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) { ui-&gt;setupUi(this); mainLoop(); } MainWindow::~MainWindow() { delete ui; } void MainWindow::mainLoop() { ... DAQmxErrChk (DAQmxRegisterSignalEvent(taskHandle,DAQmx_Val_ChangeDetectionEvent,0,ChangeDetectionCallback,NULL)); ... } int32 MainWindow::ChangeDetectionCallback(TaskHandle taskHandle, int32 signalID, void *callbackData) { ... return 0; } </code></pre> <p>So, again, I tried many wrong ways to define my callback function in the header file unsuccessfully. Please, help me to get this straight. And here's the error message that I do not clearly understand:</p> <pre><code>D:\Projects\sapm3\mainwindow.cpp:37: error: cannot convert 'MainWindow::ChangeDetectionCallback' from type 'int32 (MainWindow::)(TaskHandle, int32, void*) {aka long int (MainWindow::)(void*, long int, void*)}' to type 'DAQmxSignalEventCallbackPtr {aka long int (__attribute__((__cdecl__)) *)(void*, long int, void*)}' DAQmxErrChk (DAQmxRegisterSignalEvent(taskHandle,DAQmx_Val_ChangeDetectionEvent,0,ChangeDetectionCallback,NULL)); </code></pre> <p>Here's the original code. It triggers callback function to get a measurement sample and outputs the data to console. I wish to write the sampled data to my member variable and emit a signal that is defined in the .h file of the object.</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;string.h&gt; #include &lt;time.h&gt; #include &lt;NIDAQmx.h&gt; #define DAQmxErrChk(functionCall) if( DAQmxFailed(error=(functionCall)) ) goto Error; else static TaskHandle taskHandle; static uInt32 numLines; static uInt8 cachedData[200]; int32 CVICALLBACK ChangeDetectionCallback(TaskHandle taskHandle, int32 signalID, void *callbackData); void Cleanup (void); int main(void) { int32 error=0; char errBuff[2048]={'\0'}; /*********************************************/ // DAQmx Configure Code /*********************************************/ DAQmxErrChk (DAQmxCreateTask("",&amp;taskHandle)); DAQmxErrChk (DAQmxCreateDIChan(taskHandle,"Dev1/port0/line0:7","",DAQmx_Val_ChanPerLine)); DAQmxErrChk (DAQmxCfgChangeDetectionTiming(taskHandle,"Dev1/port0/line0:7","Dev1/port0/line0:7",DAQmx_Val_ContSamps,1)); DAQmxErrChk (DAQmxRegisterSignalEvent(taskHandle,DAQmx_Val_ChangeDetectionEvent,0,ChangeDetectionCallback,NULL)); DAQmxErrChk (DAQmxGetTaskNumChans(taskHandle,&amp;numLines)); /*********************************************/ // DAQmx Start Code /*********************************************/ DAQmxErrChk (DAQmxStartTask(taskHandle)); puts("Continuously reading. Press Enter key to interrupt\n"); puts("Timestamp Data read Changed Lines"); getchar(); Error: if( DAQmxFailed(error) ) { DAQmxGetExtendedErrorInfo(errBuff,2048); Cleanup(); printf("DAQmx Error: %s\n",errBuff); } printf("End of program, press Enter key to quit\n"); getchar(); return 0; } int32 CVICALLBACK ChangeDetectionCallback(TaskHandle taskHandle, int32 signalID, void *callbackData) { int32 error=0; uInt8 data[200]={0}; int32 numRead; uInt32 i=0; char buff[512], *buffPtr; char errBuff[2048]={'\0'}; char *timeStr; time_t currTime; if( taskHandle ) { time (&amp;currTime); timeStr = ctime(&amp;currTime); timeStr[strlen(timeStr)-1]='\0'; // Remove trailing newline. /*********************************************/ // DAQmx Read Code /*********************************************/ DAQmxErrChk (DAQmxReadDigitalLines(taskHandle,1,10.0,DAQmx_Val_GroupByScanNumber,data,8,&amp;numRead,NULL,NULL)); if( numRead ) { buffPtr = buff; strcpy(buff, timeStr); strcat(buff," "); buffPtr = buff + strlen(buff); for(;i&lt;numLines;++i) { sprintf(buffPtr,"%d",data[i]); buffPtr++; } strcat(buff," "); buffPtr = buff + strlen(buff); for(i=0;i&lt;numLines;++i) { sprintf(buffPtr,"%c",data[i]==cachedData[i]?'-':'X'); buffPtr++; cachedData[i] = data[i]; } puts(buff); fflush(stdout); } } return 0; Error: if( DAQmxFailed(error) ) { DAQmxGetExtendedErrorInfo(errBuff,2048); Cleanup(); printf("DAQmx Error: %s\n",errBuff); } return 0; } void Cleanup (void) { if( taskHandle!=0 ) { /*********************************************/ // DAQmx Stop Code /*********************************************/ DAQmxStopTask(taskHandle); DAQmxClearTask(taskHandle); taskHandle = 0; } } </code></pre> <p>I found the way to go around my problem. I declare an array variable at the top of the file. This way my callback function recognizes it. Then, I copy data from this array to my member array. Similarly, I created a counter variable and increment it each time the callback runs. At the same time I loopcheck this variable in my member function until it reaches desirable value and then emit a signal. Such approach really sucks and I wish to find a more intelligent way to writ it. </p>
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    1. COI am not sure what is unclear about the error message. You have a callback outside your call, and you want to define that inside. This is not possible. You would need to create a method at best inside your class calling the other outside. Also, what exactly do you mean by `When I tend to use some of the variables or functions that are defined in .h file, the ChangeDetectionCallback function does not recognize them.`? I do not see that callback using any member in your code...
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    2. COLaszlo, thank you for checking on my code.
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    3. COThe sample code I found is in one single .c file. I want to incorporate that code into my files. If I copy and paste that code, it works as it should, however, when I try to change it so it writes to member variables or uses members functions, it does not recognize them. Thus, I wanted to define this callback function as member as well, so it can recognize those or emit signals. Do not have any idea how to do it right.
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