Question

for my assignment I am building a heap, the data for the heap is coming from a file. One of the functions is to get the data, but I am having trouble understanding the ifstream read() function and am getting quite a nasty error because of it this is what I have:

template<class T, class P>
void get_list(vector<T>& v, const char* file_loc, P func) { 
   T data;
   ifstream inFile;

   inFile.open("file_loc");
   if (!inFile) {
      cerr << "Error - unable to open input file\n";
      exit(1);
   }

   inFile.read( &data, sizeof(T));

   while (inFile) {
      inFile.read( &data, sizeof(T));
      insert(v,data,func);
   }

   inFile.close();
}

the error I am receiving is:

prog7.h:53: error: no matching function for call to 
‘std::basic_ifstream<char, std::char_traits<char> >::read(int*, long unsigned int)’
/usr/include/c++/4.3/istream:468: note: candidates are: std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT,_Traits>::read(_CharT*, std::streamsize) 
[with _CharT = char,   _Traits = std::char_traits<char>]

any help would be much appreciated!

Answer 1

The prototype for std::ifstream::read is

istream& read ( char* s, streamsize n );

So where you have

inFile.read( &data, sizeof(T));

should be

inFile.read( (char*) &data, sizeof(T));

However this assumes you are reading raw bytes from a binary file. If you are parsing a text file with the integers represented in decimal ascii characters you can just use

inFile >> data;