Binary/Int File reading & Array Storage

You can use a loop and in each and every iteration, you will be going over each and every digit. Multiply the first digit by 2^7 and second digit by 2^6 and like that go on till your 8th digit (multiple by 2^0). Also while going through this add this number and store in a vector or array. Also, have a variable which tracks the current position on the digits. Because, after every 8 digits, you have to perform the same above said process to convert the 8 bit binary to a byte.

Well, you've already broken it down into steps:

• read 8 digits at a time to make a byte
• then store that as a int
• stuff that into an array of ints

That's great! Let's look at each.

First, you need to read the file one character at a time. The C standard library provides a function for this: fgetc. Pass in a FILE *, it'll give you back the ASCII value of the number it read, or EOF (-1) when you've hit the end of the file.

So, we know we can use fgetc, and without any line breaks, we know it'll return '1', '0', or EOF. Put another way:

10001101 => successive fgetc() calls will return
  '1', '0', '0', '0', '1', '1,' '0', '1', 'EOF'

This sounds like a loop:

for (int bits = 0; bits < 8; bits++) {
  int digit = fgetc(file);
  if (digit == '0') {
    // something
  } else if (digit == '1') {
    // something else
  } else if (digit == EOF) {
    // done with the file
  }
}

All right. Now, how do we assemble 0s and 1s into a binary number? The answer is bit shifting. We set up a variable to hold the output number, then repeatedly set the lowest bit and shift the other bits up. So:

10001101
'1' =>        1
'0' =>       10
'0' =>      100
'0' =>     1000
'1' =>    10001
'1' =>   100011
'0' =>  1000110
'1' => 10001101

So:

int number = 0;
for (int bits = 0; bits < 8; bits++) {
  // shift number up one place
  number = number << 1;

  int digit = fgetc(file);
  if (digit == '0') {
    // do nothing; the lowest bit is 0 already
  } else if (digit == '1') {
    // set number's lowest bit
    number |= 0x01;
  } else if (digit == EOF) {
    // done with the file
  }
}

Now all you need to do is wrap that in another loop that puts number in an array. That's just a matter of remembering how many numbers you've already stored (a counter), and then escaping from the loop when you hit the end of the file.

Here is a C++ example of how to write integers in binary form out to a file, and how to read the binary data back as integers in the same program. Comments are in the program, hopefully this helps.

This assumes your machine acknowledges data type char as 1 byte, and int as 4 bytes.

#include <fstream>
#include <iostream>

using namespace std;

int main() { 

    ofstream outFile; // File which we will write binary data to.
    ifstream inFile;  // File which we will read binary data from.

    outFile.open( "intBin.txt", ios::binary ); // Flag file as binary.

    for( int i = 0; i < 20; ++i ) {
            // This writes 4 bytes out to file.
        outFile.write( reinterpret_cast<const char*>(&i), sizeof(int) );
    }
    outFile.close(); // Must close, since race conditions will occur accessing same file in same process of our program.

    inFile.open("intBin.txt", ios::binary); // Flag file as binary.
    int binVals;
    for( int i = 0; i < 20; ++i ) {
            // This reads 4 bytes back into the file.
        inFile.read( reinterpret_cast<char*>(&binVals), sizeof(int) );
        cout << binVals << endl;
    }
    inFile.close();

}