c++ binary files

The_Bullman

I'm trying to make a simple rle compression program. I've inputed a text file which works fine but when I try to do the same with a bitmap it doesn't work.

I'm storing the input from the file as type char and trying to compare them using ">, <, ==". If it matches I count the number of times it does then output the variable(char), then a count(int). This all goes into another binary file.

I'm not sure if I'm explaining this properly so here's the code which should explain it better.

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

using namespace std;

typedef vector<char> CompVec;
CompVec compress;

ifstream::pos_type size;
char * memblock;
char * compress_memblock;

int i = 0;

void addToCompressVector( char c_in )
{
	compress.push_back(c_in);
}
void addToCompressVector( int c_in)
{
	compress.push_back(c_in);
}

int fillMemory()
{
	//ifstream fileIn ("test.txt", ios::in|ios::binary|ios::ate);
	ifstream fileIn ("test.bmp", ios::in|ios::binary|ios::ate);

	if( fileIn.is_open() )
	{
		size = fileIn.tellg();

		//debug
		cout << "input file size: " << size << "bytes" << endl;

		memblock = new char [size];
		fileIn.seekg (0, ios::beg);
		fileIn.read (memblock, size);
		fileIn.close();

		int num = size;
		return num;
	}
	else
	{
		return -1;
	}
}

char getc()
{
	if( i > ((int)size - 1))
	{
		return NULL;
	}
	else
	{
		char getChar;
		getChar = memblock[i];
		i++;
		
		return getChar;
	}
}

void rleCompress()
{
    char last = -1;
    char lastbo = -2;
	char c;

	int num = fillMemory();
	if ( num != -1 )
	{
		while((c = getc()) != NULL)
		{
			addToCompressVector(c);

			if (lastbo == last)
			{
				if (c == last)
				{
					int count = 0;

					while (( c = getc()) != NULL )
					{
						if (c == last)
						{
							count++;
						}
						else
						{
							break;
						}
					}

					if( count >= 0 )
					{
						addToCompressVector(count);
					}

					if( c >= 0 )
					{
						addToCompressVector(c);
					}
				}
			}
			lastbo = last;
			last = c;
		}

	}
	else
	{
		cout << "unable to open file"<< endl;
	}
}

void outputCompress()
{
	ofstream fileOut ("test.dat");

	if (fileOut.is_open())
	{
		int compress_memblock_size = compress.size();
		compress_memblock = new char[compress_memblock_size];
		for( int loop_i = 0; loop_i < compress_memblock_size; loop_i ++ )
		{
			compress_memblock[loop_i] = compress.at(loop_i);
		}
		fileOut.write( compress_memblock, compress_memblock_size );
		fileOut.close();

		delete[] memblock;
	}
	else
	{
		cout << "unable to open file"<< endl;
	}
}

int main ()
{
	cout << "run rleCompress()" << endl;
	rleCompress();
	cout << "\nrun outputCompress()" << endl;
	outputCompress();

	cin.get();
	return 0;
}

When I run this with the bitmap as the input file it will only loop 5 times then break when it shouldn't(I think)

Any ideas where its messing up on me?

bpmurray

while((c = getc()) != NULL)

What happens if you have a byte in the file that is actually 0x00? This is something that isn't just likely: it's inevitable!

Maybe a better way would be to return a 16-bit value from the getc function, and setting the high bit if you've hit EOF.