I have to read some .mat data files from c++, I read through the documentation, but I would like to know how to handle the data in a clean and elegant way, e.g. using std:vector(modest .mat file size(10M~1G), but memory issues should be taken seriously)
My function is sth like:
#include <stdio.h>
#include "mat.h"
#include <vector>
int matread(const char *file, const vector<double>& pdata_v) {
MATFile *pmat;
pmat=matOpen("data.mat","r");
if (pmat == NULL) {
printf("Error opening file %s\n", file);
return(1);
}
mxArray *pdata = matGetVariable(pmat, "LocalDouble");
// pdata -> pdata_v
mxDestroy pa1; // clean up
return 0;
}
so, the question is, how can I make a copy from mxArray *pdata array to vector pdata_v efficiently and safely?
Here is an example of using the MAT-API:
#include "mat.h"
#include <iostream>
#include <vector>
void matread(const char *file, std::vector<double>& v)
{
// open MAT-file
MATFile *pmat = matOpen(file, "r");
if (pmat == NULL) return;
// extract the specified variable
mxArray *arr = matGetVariable(pmat, "LocalDouble");
if (arr != NULL && mxIsDouble(arr) && !mxIsEmpty(arr)) {
// copy data
mwSize num = mxGetNumberOfElements(arr);
double *pr = mxGetPr(arr);
if (pr != NULL) {
v.reserve(num); //is faster than resize :-)
v.assign(pr, pr+num);
}
}
// cleanup
mxDestroyArray(arr);
matClose(pmat);
}
int main()
{
std::vector<double> v;
matread("data.mat", v);
for (size_t i=0; i<v.size(); ++i)
std::cout << v[i] << std::endl;
return 0;
}
First we build the standalone program, and create some test data as a MAT-file:
>> mex -client engine -largeArrayDims test_mat.cpp
>> LocalDouble = magic(4)
LocalDouble =
16 2 3 13
5 11 10 8
9 7 6 12
4 14 15 1
>> save data.mat LocalDouble
Now we run the program:
C:\> test_mat.exe
16
5
9
4
2
11
7
14
3
10
6
15
13
8
12
1