CODEWITHSUNDEEP
c++arraysmatlabmatrix
Gilad
Gilad

Reputation: 6575

transforming c++ array to matlab big matrix using file

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?

Upvotes: 1

Views: 164

Answers (2)

Rattus Ex Machina
Rattus Ex Machina

Reputation: 462

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").

Upvotes: 2

user4581301
user4581301

Reputation: 33932

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.

Upvotes: 2

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