Question

I need to write this in Java.

Although I know how to read a file, I’m interested in what the ‘buff’ output is, is the length at the beginning?

char              *buff;
unsigned char     *aux;


while(fgets (buff+2, length, fin)){
    len = strlen (buff + 2) + 2;
    aux = (unsigned char *) &len;
    buff[1] = aux[0];
    buff[0] = aux[1];
    ...
    send (sd, buff, len, 0);

}

but I don’t understand this:

aux = (unsigned char *) &len;
buff[1] = aux[0];
buff[0] = aux[1];

Thanks in advance.

Answer 1

This code:

aux = (unsigned char *) &len;
buff[1] = aux[0];
buff[0] = aux[1];

creates a byte-array view of the integer value stored in len. In Java, you can’t do exactly the same thing, but you can get what you want a couple of ways. The easiest is just with bit masking and shifting:

int len = ...;
byte[] buff = ...;
byte[0] = (byte) (len & 0xff);
byte[1] = (byte) ((len >> 8) & 0xff);

Another possibility is to use a ByteBuffer, but that seems overkill for such a simple operation.