Question

My main question is about how you read data from a file that is not of the char data type.
I am writing a file of data from MATLAB as follows:

x=rand(1,60000);
fID=fopen('Data.txt','w');
fwrite(fID,x,'float');
fclose(fID);

Then when I try to read it in C++ using the following code “num” doesn’t change.

#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    fstream fin("Data.txt",ios::in | ios::binary);
    if (!fin)
    {   
        cout<<"\n Couldn't find file \n";
        return 0;
    }
    float num=123;
    float loopSize=100e3;
    for(int i=0; i<loopSize; i++)
    {
        if(fin.eof())
        break;

        fin >> num;
        cout<< num;
    }
    fin.close();
    return 0;
}

I can read and write file in matlab fine, and I can read and write in c++, but I can’t write in matlab and read in c++. The files I write in matlab are in the format I want, but the files in c++ seem to be writing/reading the numbers out at text. How do you read a series of floats in from a file in C++, or what am I doing wrong?

edit: The loop code is messy because I didn’t want an infinite loop and the eof flag was never being set.

Answer 1

Formatted I/O using << and >> does indeed read and write numeric values as text.

Presumably, Matlab is writing the floating-point values in a binary format. If it uses the same format as C++ (most implementations of which use the standard IEEE binary format), then you could read the bytes using unformatted input, and reinterpret them as a floating-point value, along the lines of:

float f;  // Might need to be "double", depending on format
fin.read(reinterpret_cast<char*>(&f), sizeof f);

If Matlab does not use a compatible format, then you’ll need to find out what format it does use and write some code to convert it.