segmentation error

[swethapradeep]

Hello,

I have class IMAGEINFO which stores information about BMP image.

      
 class IMAGEINFO
          {
             int IMfilesize;
             int IMheight;
             int IMwidth;
             int IMbitsperpixel;
             int IMnoofcolors;
             unsigned char IMcolortable;
             int IMvectorsize;
             char* IMheader;
            char* IMrasterdata;
            public:
            IMAGEINFO();
           ~IMAGEINFO();
           void getimageheader(ifstream&);
           void getcolortable(ifstream&);
           void getrasterdata(ifstream&);
           void getimageinfo(string);
           void putimageheader(ofstream&);
           void putcolortable(ofstream&);
           void writeimageinfo(string);
        };
         
  
        
           void IMAGEINFO::putimageheader(ofstream& file)
            {
               int counter;
   
              for(counter=0;(IMheader+counter)!=NULL;counter++)
              {
                  file.write((IMheader+counter),sizeof(char));
              }

}



I get a segmentation error:
Program received signal SIGSEGV, Segmentation fault.
0xb7d398aa in memcpy () from /lib/tls/i686/cmov/libc.so.6


I know that the segmentation error i happening because the program i trying to access an unallocated memory. I have checked if it is NULL .
I would like to know why it is happenning?
-thankyou
swetha

[GNU-Fan]

What is it that you want to achieve with this statement?

(IMheader+counter)!=NULL

[swethapradeep]

Hi,

void  IMAGEINFO::getimageheader(ifstream& filenm)
{
   int counter=0,index;
   if(filenm.is_open())
   {
      filenm.seekg(2,ios::beg);
      filenm.read((char*)&IMfilesize,sizeof(int));
      cout<<"The filesize is"<<IMfilesize<<"\n";
      filenm.seekg(18,ios::beg);
      filenm.read((char*)&IMwidth,sizeof(int));
      cout<<"The width is"<<IMwidth<<"\n";
      filenm.seekg(22,ios::beg);
      filenm.read((char*)&IMheight,sizeof(int));
      cout<<"The height is"<<IMheight<<"\n";
      filenm.seekg(28,ios::beg);
      filenm.read((char*)&IMbitsperpixel,sizeof(int));
      cout<<"Bits per pixel-"<<IMbitsperpixel<<"\n";
      filenm.seekg(46,ios::beg);
      filenm.read((char*)&IMnoofcolors,sizeof(int));
      cout<<"Number of colors-"<<IMnoofcolors<<"\n";
      filenm.seekg(0,ios::beg);
      IMheader=new unsigned char[53];

      while(filenm.tellg()<54)
      {
        filenm.read((char*)&IMheader[counter],sizeof(char));
       counter=counter+1;
      }
}

I have allocated memory for IMheader.
so, i expect (IMheader+54)==NULL.i.e when the counter value is 54 i expected the value to be NULL.
-swetha

[GNU-Fan]

so, i expect (IMheader+54)==NULL.i.e when the counter value is 54 i expected the value to be NULL.

But IMheader is a pointer to char, i.e. a number that is a memory address. This number can be anything from 0 to about 2^32 or more. If you add 54 to it, it is certainly not NULL

Dereferencing you do with a leading '*', or you employ the array index operator '[]'.

[Rubberman]

Show your implememtation of the constructors for the IMAGEINFO class. A common newbie C++ programming error is failure to properly initialize member variables, especially pointers. In your case, if you don't initialize it, the pointer is a random bunch of bits - crash is your best hope. If you initialize it to 0 (null) and this is a valid state, then you need to test for null in your code. If it must be initialized when the object is created, then make sure you have done so, but also that you delete it in your destructor (otherwise you end up with a memory leak).