reading C++ binary file in Java

Question

I have a 500MB binary file. with a bunch of float entries. It was written by a C++ program. I would load it in C++ like this.

void load(char f_name[], int size, float data[])
{
    std::fstream f_bin(f_name, std::ios::in|std::ios::binary);

    f_bin.seekg(std::ios::beg);
    f_bin.read((char*)data, size*sizeof(float));
    f_bin.close();
}

float *data;
int size = 123456789;
data = new float[size];
load("myFile.bin", size, data);

And i can access the float values: data[x]; In c++ it works preatty fast. Is there something simular in java?

Edit After reading a bit around i have this so far:

        RandomAccessFile f = new RandomAccessFile("C://path//myFile.bin", "r");
        byte[] bytes = new byte[(int)f.length()];
        f.read(bytes);

        float fl = ByteBuffer.wrap(bytes).order(ByteOrder.LITTLE_ENDIAN).getFloat();     


        System.out.println(fl);

Which prints the first float entry. Now i should loop float by float and put it in an array like float[] data.

Answer 1

You can do this in Java.

try(FileChannel fc = new RandomAccessFile("myFile.bin", "rw").getChannel()) {
    FloatBuffer fb = fc.map(MapMode.READ_WRITE, 0, fc.size())
                       .order(ByteOrder.nativeOrder()).asFloatBuffer();
    // use fb 
}

This is quite a bit faster as it memory maps the file and avoids a memory copy (you can do the same in C++)