Reading a data file with int16 short

[Donnafoo]

I am trying translate a code from Matlab into C++. I am stuck at the most basic of steps: loading in a data file of int16. I know how to do it Matlab (its just one line of code). I even did it in C (although I still don't know how I got that to work, but it does). Any suggestions would be greatly appreciated.

Here is my C++ code:

#include <iostream>
#include <fstream>
#include <stdint.h>
using namespace std;

int main()
{
int i;

std::ifstream ifs ("/filepath/filename.hdr", ios::binary);


for(i=0;i<24;i++){

cout << (int16_t) ifs.get()<<endl;
}
ifs.close();}

The output is:

92 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

But it should be:

348 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 114 4 999 665 1090

The output and input is actually all on separate lines, but I put it all on one line for easier reading here.

To read the data in Matlab it is just:

[data,~]=fread(fid,'short');% fid is the file ID (pointer)

And to read the file in C it is:

#include <stdio.h>

int main () {
FILE *header;
union twobytes // I found this method online and adapted it
{
int intvalue;
char byte [sizeof (int)];
 } bytes;

int lSize; 
int result;
int i;

header=fopen("filepath/file.hdr","rb"); // it is an .hdr file
fseek (header, 0, SEEK_END); 
lSize = ftell (header);
printf("file size %i\n",lSize);  // size of the file
rewind (header); // go back to start
char buffer[4];
for(i=0;i<24;i++){ // only need first 25 values
result=fread (buffer, 2, 1, header); // no idea why it is 1 and not 2, but 2 didn't work
printf("buffer is:%i\n",*buffer); // this buffer actually give me 92 if I print it to screen without the below modification. the same value as the first output in the C++ code
bytes.byte[0] = buffer[0];
bytes.byte[1] = buffer[1];
bytes.byte[2] = 0;  // no idea why but this is necessary for it to work
bytes.byte[3] = 0;
printf ("\nbytes.intvalue: %i\n", bytes.intvalue);


}

fclose(header);

return 0;
}

It is so much easier to do in Matlab, but I am working with 3D images and need to move the code to something with better memory. I am trying to read in the header file with the dimensions of the image matrix. I have been working on this for two days and cannot figure it out! It has been great to learn more about C++ coding, I just wish I knew as much about coding in it as I do about Matlab.

[Duthomhas]

istream::get() reads only one byte. You need to read two. Your other codes will fail if you try to load negative int16_t's. It will also fail if you try to compile on a system using a different endianness.

int16_t n = 0;
n |= (unsigned char)ifs.get();
n |= ifs.get() << 8;
cout << n << endl;

Hope this helps.

[Donnafoo]

It works! Thanks for explaining it also, this is a real learning curve for me.

[Duthomhas]

Everything I do is a learning curve. You get used to always learning before too long.