Saving the parameters returned from mex
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The timestamp from my mex file is passed back to mat file as data. I encountered that it saves the first and the last data it receives and the rest all zeros. How do i edit my mat file to ensure i get all the values? I guess the problem lies with the data=zeros(1,1) and the return parameter that is data. how do i change it?
Mat File:
clear;clc;
config;
data = zeros(1,1);
[status, validity, data] = readGPS(OPEN,'gps-2011-10-13-15-15.log');
index = 1;
while(status ~= STOP)
[status, validity, data] = readGPS(READ);
if validity == VALID_DATA
data(:,index) = data;
index = index + 1;
end
save('gpstime.mat','data')
end
Mex File:
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 = NO_VALUE;
if (fid != NULL)
{
status = CONTINUE;
}
else
{
status = STOP;
}
break;
case READ:
if(!feof(fid))
{
status = CONTINUE;
validity = VALID_DATA;
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);
}
break;
case CLOSE:
fclose(fid);
validity = INVALID;
timestamp = NO_VALUE;
status = STOP;
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[0] = validity;
plhs[2] = mxCreateDoubleMatrix(1,1,mxREAL);
data_out = mxGetPr(plhs[2]);
data_out[0] = timestamp;
}
0 个评论
回答（1 个）
Friedrich
2012-1-3
Hi,
the problem is that you use the variable data for two different things. To store the overall data and as returnvalue of that mex file. Try it like this:
clear;clc;
config;
data = zeros(1,1);
[status, validity, data] = readGPS(OPEN,'gps-2011-10-13-15-15.log');
index = 1;
while(status ~= STOP)
[status, validity, tmp] = readGPS(READ);
if validity == VALID_DATA
data(:,index) = tmp;
index = index + 1;
end
end
save('gpstime.mat','data')
Is there a reason why you are doing this with a mex file? You can do this in MATLAB directly pretty easy.
5 个评论
Jw
2012-1-3
Friedrich
2012-1-3
thanks for the clarification. So your issue is solved now?
Jw
2012-1-4
Friedrich
2012-1-4
Could you please mark it as accepted than? Thanks.
Titus Edelhofer
2012-1-4
Just a comment: for the last lines of your mex file you might also use mxCreateDoubleScalar ...
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