Tuenti Contest 14 (Pablo Moreno)

/*
    Author: Pablo Moreno Olalla
    Email address: darthbrevu@yahoo.es
*/
#include <cstdio>
#include <string>
#include <sstream>
#include <iostream>
#include <stdint.h>
#include <stdexcept>

using namespace std;

//This code is a little too ad hoc, which means that you shouldn't use it for general BMP files!
class Bmp24bits {
private:
    uint32_t width;
    uint32_t height;
    unsigned char **r;
    unsigned char **g;
    unsigned char **b;
public:
    Bmp24bits(const char *fn)   {
        uint32_t ptr;
        FILE *fd=fopen(fn,"rb");
        if (!fd) throw runtime_error("Couldn't open file.");
        fseek(fd,10,SEEK_SET);
        fread(static_cast<void *>(&ptr),4,1,fd);
        fseek(fd,4,SEEK_CUR);
        // Reading both width and height seems like a good trick, but may be unsafe due to alignment issues.
        // It would work on most computers, though.
        fread(static_cast<void *>(&width),4,1,fd);
        fread(static_cast<void *>(&height),4,1,fd);
        r=new unsigned char *[height];
        g=new unsigned char *[height];
        b=new unsigned char *[height];
        fseek(fd,ptr,SEEK_SET);
        unsigned char *tmpbuf=new unsigned char[3*width];
        for (int i=height-1;i>=0;--i)   {
            r[i]=new unsigned char[width];
            g[i]=new unsigned char[width];
            b[i]=new unsigned char[width];
            unsigned char *rt=r[i];
            unsigned char *gt=g[i];
            unsigned char *bt=b[i];
            fread(static_cast<void *>(tmpbuf),1,3*width,fd);
            unsigned char *p=tmpbuf;
            for (size_t j=0;j<width;++j)    {
                bt[j]=p[0];
                gt[j]=p[1];
                rt[j]=p[2];
                p+=3;
            }
        }
        delete[] tmpbuf;
        fclose(fd);
    }
    ~Bmp24bits()    {
        for (size_t i=0;i<height;++i)   {
            delete[] r[i];
            delete[] g[i];
            delete[] b[i];
        }
        delete[] r;
        delete[] g;
        delete[] b;
    }
    inline unsigned int computeSum(char component,size_t row) const {
        if (row>height) return 0;
        const unsigned char *p;
        if (component=='r'||component=='R') p=r[row];
        else if (component=='g'||component=='G') p=g[row];
        else if (component=='b'||component=='B') p=b[row];
        else return 0;
        unsigned int res=1; //It seems that I must do this (instead of res=0), but I don't understand why :(.
        for (size_t i=0;i<width;++i) res+=static_cast<unsigned int>(p[i]);
        return res;
    }
    inline uint32_t getWidth() const    {
        return width;
    }
    inline uint32_t getHeight() const   {
        return height;
    }
};

int main(int argc,char **argv)  {
    const char *fn;
    fn=((argc<=1)?"trabaja.bmp":argv[1]);
    //The following two lines are not strictly necessary, but make the code a little more handy.
    if (argc>=3) freopen(argv[2],"r",stdin);
    if (argc>=4) freopen(argv[3],"w",stdout);
    Bmp24bits bm(fn);
    string tmp;
    char c;
    unsigned int line;
    do  {
        getline(cin,tmp);
        if (sscanf(tmp.c_str(),"%c%u",&c,&line)!=2) break;
        else cout<<bm.computeSum(c,line)<<endl;
    }   while (!cin.eof());
    return 0;   //bm will be deleted and freed automatically, so no need to do it explicitly :).
}