unformatted input to a std::string instead of c-string from binary file.

Question

ok i have this program working using c-strings. I am wondering if it is possible to read in blocks of unformatted text to a std::string? I toyed arround with if >> but this reads in line by line. I've been breaking my code and banging my head against the wall trying to use std::string, so I thought it was time to enlist the experts. Here's a working program you need to supply a file "a.txt" with some content to make it run.

i tried to fool around with:

in.read (const_cast<char *>(memblock.c_str()), read_size);

but it was acting odd. I had to do std::cout << memblock.c_str() to get it to print. and memblock.clear() did not clear out the string.

anyway, if you can think of a way to use STL I would greatly appreciate it.

Here's my program using c-strings

// What this program does now:  copies a file to a new location byte by byte
// What this program is going to do: get small blocks of a file and encrypt them
#include <fstream>
#include <iostream>
#include <string>

int main (int argc, char * argv[]) 
{
 int read_size = 16;
 int infile_size;
 std::ifstream in;
 std::ofstream out;
 char * memblock;
 int completed = 0;

 memblock = new char [read_size];
 in.open ("a.txt", std::ios::in | std::ios::binary | std::ios::ate);
 if (in.is_open())
  infile_size = in.tellg();
 out.open("b.txt", std::ios::out | std::ios::trunc | std::ios::binary);

 in.seekg (0, std::ios::beg);// get to beginning of file

 while(!in.eof())
 {
  completed = completed + read_size;
  if(completed < infile_size)
  {
   in.read (memblock, read_size);
   out.write (memblock, read_size);
  } // end if
  else // last run
  {
   delete[] memblock;
   memblock = new char [infile_size % read_size];
   in.read (memblock, infile_size % read_size + 1);
   out.write (memblock, infile_size % read_size );
  } // end else
 } // end while
} // main

if you see anything that would make this code better please feel free to let me know.

Answer 1

Rather than using a std::string, consider using a std::vector<char>; that gets you around all the problems with doing a const_cast on the result of calling std::string::c_str(). Just resize the vector to whatever size you need before you start using it.

If you want to print the contents, you can null-terminate the contents of the vector by pushing a null-terminator onto the back:

std::vector<char> v;
v.push_back('\0');
std::cout << &v[0];

or you can convert it into a std::string:

std::vector<char> v;
std::string s(v.begin(), v.end());

This all assumes that you have some block of text that you want to read from a binary file. If you are trying to print out binary characters, this won't work, obviously. It wasn't entirely clear from your question.