Mex

Apologise for my previous post as I posted the wrong coding. I have this error One or more output arguments not assigned during call to "readData". pls assist to let me know where to correct the error. Thanks all.

Error in ==> main at 6 [status, validity, data] = readData(OPEN,'gps-2011-10-13-15-15.log');

clear;
config;

data = zeros(1,1);

[status, validity, data] = readData(OPEN,'gps-2011-10-13-15-15.log');
index = 1;

while(status ~= EOF)
   [status, validity, data] = readData(READ);
   if validity == VALID_DATA
       data(:,index) = data;
       index = index + 1;
   end
end

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Mex file

===================================

    #define OPEN 0
    #define CLOSE 1
    #define READ 2
    #define VALID_DATA 1
    #define INVALID -1
    #include "mex.h"
    #include <stdlib.h>
    #include <stdio.h>
    #include <string.h>
    #include <math.h>
    #include <matrix.h>

double timestamp;
int status, validity;
FILE *fid; 
void mexFunction(int nlhs, mxArray *plhs[],int nrhs, const mxArray *prhs[])
{
   int Op;
   double *status_out, *validity_out, *data_out;
   char data [17], buffer [256];
   char *str;

     /*check to find out the operation required*/
     if (nrhs == 2)
     {
         Op = OPEN;
     }
     else
     {
         Op = READ;
     }

     /*Different cases for different operations*/
     switch (Op)
     {
          case OPEN:
              fid=fopen("gps-2011-10-13-15-15.log","r");  //open file as read   
              validity = INVALID;
              timestamp = -1;
              if (fid != NULL)
              {
                  status = 1;
              }
              else
              {
                  status = -1;
              }

              return;

          case READ:
            while(!feof(fid))
            {
                fgets(buffer, 255, fid);          //read in the first line of the file
                str = strtok(buffer, ",");        //get the timestamp 
                strcpy(data, str);            
                timestamp = atof(data);           //change from char to double
                mexPrintf("Timestamp:%f \n",timestamp);
            }           
            return;

          case CLOSE:
              fclose(fid);
              timestamp = -1;
              validity = INVALID;
              break;

          default:
        mexErrMsgTxt("Incorrect parameter 3.");
              break;
      }   

     /*Passing back results*/
      plhs[0] = mxCreateDoubleMatrix(1,1,mxREAL); //create an mxArray
      status_out = mxGetPr(plhs[0]);              //get a pointer to the data
      status_out[0] = status;

      plhs[1] = mxCreateDoubleMatrix(1,1,mxREAL);
      validity_out = mxGetPr(plhs[1]);
      validity_out[1] = validity;

      plhs[2] = mxCreateDoubleMatrix(1,1,mxREAL);
      data_out = mxGetPr(plhs[2]);
      data_out[2] = timestamp;

      mxFree(status_out);
      mxFree(validity_out);
      mxFree(data_out);        
  }

Answer 1

[Friedrich]

Hi,

I think the issue is raised in your switch statement when you open a file. You have a return in there, which leads to terminating the mex file without assigning the output variables. Change the return to a break and it should work.

In addition these line should generate a SegV:

plhs[1] = mxCreateDoubleMatrix(1,1,mxREAL);
      validity_out = mxGetPr(plhs[1]);
      validity_out[1] = validity;

Since validity_out[1] will access the second field in an array with one field only. This should be

validity_out[0] = validity;

The same applies on timestamp.

You dont need to apply mxFree on the xx_out variables. Since the weren't allocated woth mxMalloc and in addition they get deleted automatically when the mex function is finshed running.

[Jw]

thank you

[Jw]

I have multiple timestamps and when i return to my matlab, it only stores the 1st. I think the problem lies with the data = zeros(1,1) and the return of my [status, validity, data]. how do i create a temp storage for the data coming in so that i can get all my data into matlab?

Answer 2

[Titus Edelhofer]

Hi,

the return statements in the switch-case block are suspicious: you are leaving the mex file without entering the "passing back results" section. I guess you need to replace them by "break" ...?

Titus

[Titus Edelhofer]

BTW: why do you write this as a MEX file? Using more or less the same MATLAB code should be easier ...

Answer 3

[James Tursa]

The "return" statement error was pointed out several days ago in OP's previous thread, it just wasn't corrected. In addition, the mxFree statements at the end will likely cause a seg fault and should be removed. And a mexAtExit function should be registered to close the file in the case that the mex function gets cleared before a CLOSE is processed. The data_out[2] = timestamp will also cause a seg fault, should be data_out[0]. That being said, the output variables would be much simpler if mxCreateDoubleScalar were used instead of all the mxGetPr pointer stuff.