MATLAB: Mex

dataMATLABmex

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
===================================
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);        
  }

Best Answer

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.
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