How to read in binary data and cast to unsigned char (C++)

Question

I have a raw image file that is saved in binary data (no encoding). I want to read in the file and cast the values to an unsigned char. But I'm not sure how to begin going about doing this. Each file contains 640x480 bytes. Each pixel is 8bits.

I've used the C++ help page here: http://www.cplusplus.com/doc/tutorial/files/, however when I am couting the data, it seems to be showing the same binary/non-human readable characters. Can someone please advise? Here is my code so far:

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

ifstream::pos_type size;
char * memblock;

int main () {
  ifstream file ("imageData.raw", ios::in|ios::binary|ios::ate);
  if (file.is_open())
  {
    size = file.tellg();
    memblock = new char [size];
    file.seekg (0, ios::beg);
    file.read (memblock, size);

    cout << "the complete file content is in memory";

    for (int l=0; l<size; l++){
    cout << " memblock[] is = " << (unsigned char)memblock[l] << " index was l = " << l << endl;
    }

    file.close();


    delete[] memblock;
  }
  else cout << "Unable to open file";
  return 0;
}

Here is a sample capture of the output:

 memblock[] is = ▀ index was l = 2937
 memblock[] is = E index was l = 2938
 memblock[] is = τ index was l = 2939
 memblock[] is = C index was l = 2940
 memblock[] is = ┘ index was l = 2941
 memblock[] is = B index was l = 2942
 memblock[] is = ╬ index was l = 2943
 memblock[] is = D index was l = 2944
 memblock[] is = ┼ index was l = 2945
 memblock[] is = C index was l = 2946
 memblock[] is = ╝ index was l = 2947
 memblock[] is = B index was l = 2948
 memblock[] is = ┤ index was l = 2949
 memblock[] is = B index was l = 2950
 memblock[] is = ¿ index was l = 2951
 memblock[] is = > index was l = 2952
 memblock[] is = í index was l = 2953
 memblock[] is = ; index was l = 2954
 memblock[] is = £ index was l = 2955
 memblock[] is = 6 index was l = 2956
 memblock[] is = á index was l = 2957
 memblock[] is = 4 index was l = 2958
 memblock[] is = Ñ index was l = 2959
 memblock[] is = 7 index was l = 2960
 memblock[] is = ╡ index was l = 2961

trumank · Accepted Answer · 2012-06-26 19:57:07Z

9

unsigned char* memblock; // change declaration of memblock

...

memblock = new unsigned char[size]; // change to unsigned char
file.seekg (0, ios::beg);
file.read ((char*)memblock, size); // cast to a char* to give to file.read

To print numeric values instead of characters, cast to an int before printing.

(int) memblock[l]

edited Jun 26, 2012 at 19:57

answered Jun 26, 2012 at 19:39

trumank

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11 Comments

c0d3rz Over a year ago

Hmm, MathWizz, that gives me an int instead. I want to convert it to an unsigned char (0 to 255). Is there no way to do it? Do I need to convert it to an int only?

trumank Over a year ago

What is the expected output? Are you only casting to print a numeric value?

c0d3rz Over a year ago

No, I want to deal with unsigned chars. I get raw images that are saved in binary. I just can't wrap my head around dealing with that non-readable format, so I want to work with unsigned chars just so that I can see what is happening. I was only casting for debugging for now. But I want the memblock to essentially convert all those values to unsigned chars instead ...

trumank Over a year ago

So you want to convert memblock to an unsigned char*?

c0d3rz Over a year ago

The problem with that is file.read expects a char as input parameter1: istream& read ( char* s, streamsize n ); (cplusplus.com/reference/iostream/istream/read) , so I will run into compile errors ...

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