transforming c++ array to matlab big matrix using file

Question

In my code i'm changing my array (int*) and then I want to compare it into the matlab results.

since my array is big 1200 X 1000 element. this takes forever to load it into matlab

i'm trying to copy the printed output file into matlab command line...

for (int i = 0; i < _roiY1; i++)
{
    for (int j = 0; j < newWidth; j++)
    {
        channel_gr[i*newWidth + j] = clipLevel;
    }
}

ofstream myfile;
myfile.open("C:\\Users\\gdarmon\\Desktop\\OpenCVcliptop.txt");
for (int i = 0; i <  newHeight ; i++)
{
    for (int j = 0; j < newWidth; j++)
    {
        myfile << channel_gr[i * newWidth + j] << ", ";
    }
    myfile<<";" <<endl;
}

is there a faster way to create a readable matrix data from c++? into matlab?

Rattus Ex Machina · Accepted Answer · 2015-05-11 21:22:38Z

2

The simplest answer is that it's much quicker to transfer the data in binary form, rather than - as suggested in the question - rendering to text and having Matlab parse it back to binary. You can achieve this by using fwrite() at the C/C++ end, and fread() at the Matlab end.

int* my_data = ...;
int my_data_count = ...;

FILE* fid = fopen('my_data_file', 'wb');
fwrite((void*)my_data, sizeof(int), my_data_count, fid);
fclose(fid);

In Matlab:

fid = fopen('my_data_file', 'r');
my_data = fread(fid, inf, '*int32');
fclose(fid);

It's maybe worth noting that you can call C/C++ functions from within Matlab, so depending on what you are doing that may be an easier architecture (look up "mex files").

edited May 11, 2015 at 21:22

answered May 11, 2015 at 20:38

Rattus Ex Machina

4622 silver badges8 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

user4581301 · Accepted Answer · 2015-05-11 21:21:03Z

2

Don't write the output as text.

Write your matrix into your output file the way Matlab likes to read: big array of binary.

ofstream myfile;
myfile.open("C:\\Users\\gdarmon\\Desktop\\OpenCVcliptop.txt", ofstream::app::binary);
myfile.write((char*) channel_gr, newHeight*newWidth*sizeof(channel_gr[0]));

You may want to play some games on output to get the array ordered column-row rather than row-column because of the way matlab likes to see data. I remember orders of magnitude improvements in performance when writing mex file plug-ins for file readers, but it's been a while since I've done it.

answered May 11, 2015 at 21:21

user4581301

34.1k7 gold badges42 silver badges65 bronze badges

Collectives™ on Stack Overflow

transforming c++ array to matlab big matrix using file

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related