Question

How is data stored when read in using fstream class? An example will clarify my question:

    char * memBlock = NULL;
    fileSize = file.tellg();
    memBlock = **new** char[fileSize];
    file.seekg(0, ios::beg);
    file.read(memBlock, fileSize);
    file.close();

    if(memBlock)
    return memBlock;

The context is that I am reading a raw image that has been recorded in hex so that

• the values representing the pixels are either 00 or ff (black or white, 1 or 0)
• and are arranged in columns and rows.

When reading the file in memory, are the values in the memblock array stored as ff and 00 or are they converted into 1 and 0 automatically by ASCII or something?

Answer 1

When the data is stored as hex

00FF00FF

and you read it using file.read as shown in your code,
then it is stored as that, which means that

memcmp(memblock, "00FF00FF", 8) == 0

will evaluate to true.

EDIT

You have to make the conversion yourself. One way would be

int ConvertToColor(const char *colorBuffer, size_t size)
{
    int color = -1;
    if(size >= 2)
    {
        char colorCode[3] = { colorBuffer[0], colorBuffer[1], 0 };
        long longColor = strtol(colorCode, NULL, 16);
        if(longColor != LONG_MAX && longColor != LONG_MIN)            
            color = (int)longColor;

    } 
    return color;   
}

std::vector<int> ConvertToColors(const char *memBlock, size_t size)
{
    std::vector<int> colors;
    for(size_t i = 0; i < size; i += 2)
    {
        int color = ConvertToColor(memBlock + i, size - i);
        if(color < 0)
            throw std::exception("Unable to convert color.");
        colors.push_back(color ? 1 : 0);
    }
    return colors;
}