function works properly for small datasets but i have problem with

[pilafi]

void CSVImageIO::Read( void * buffer)
{ 
    char onedataline[8000000];
    char *tmp=0;
    double d=0;
    unsigned short data=0;
    unsigned short * inptr = static_cast< unsigned short * >( buffer );
    unsigned short * tmp_buf=0;
 
    //copy the pointer to the buffer, because we are going to change the pointer soon
    tmp_buf=inptr;
 
    //print the data for check
    std::ofstream     m_OutputStream("D:\\MIP\\outdata.csv");
 
    //open file
    this->m_InputStream.open(this->m_FileName.c_str(), std::ios::in);
 
    //seek to data position
    m_InputStream.seekg(data_position);
 
 
 
    int i=0,j=0,k=0;
 
 
    do 
    {    
        memset(onedataline,0,8000000);
        m_InputStream.getline(onedataline, 8000000, '\n');
        tmp=(char*)onedataline;
        while(get_next_double(&tmp,&d)==0)
        {
            data=(unsigned short)((double)fabs(d)*10000);
            *(tmp_buf++)=data; //here is the error message
            i++;
            m_OutputStream << data << " ";
        }
 
            m_OutputStream <<endl;
 
        //m_InputStream.getline(onedataline, 65000, '\n');
    }while(!m_InputStream.eof());
 
    std::cout << "data read: " << i << std::endl;
 
 
 
 
  this->m_InputStream.close(); 
} 
 

This function works properly for small datasets but i have problem with
large datasets and i get the follow error message.
I get this error message:Unhandled exception at 0x004d4286 in US.exe: 0xC0000005: Access violation writing location 0x0ad28000.

Please, if anybody knows, help me..
Thnx guys!!

[Savage]

This function works properly for small datasets but i have problem with
large datasets and i get the follow error message.
I get this error message:Unhandled exception at 0x004d4286 in US.exe: 0xC0000005: Access violation writing location 0x0ad28000.

How do you allocate the buffer,which is passed as function argument?
Also allocatin 8e6 bytes,is not a good idea,allocate it dynamically instead.

PS:Please use code tags around your code.