fstream to const char *

Question

What I want to do is read a file called "test.txt", and then have the contents of the file be a type const char *. How would one do this?

Answer 1

#include <string>
#include <fstream>

int main()
{
   std::string line,text;
   std::ifstream in("test.txt");
   while(std::getline(in, line))
   {
       text += line + "\n";
   }
   const char* data = text.c_str();
}

Be careful not to explicitly call delete on data

Answer 2

You need to:

1. create a function returning a const char*
2. open an fstream on the file
3. seek to its end
4. determine the file length by looking at the file position (tell)
5. seek back to the beginning
6. create a char* to contain the file contents
7. read the file contents into the char*
8. return the char* pointer, with the function return adding the const
9. the file is closed automatically by the fstream going out of scope

Answer 3

It's highly unlikely you really want to do that. The contents of the file (which may be either text, or binary data) are unlikely to represent a (valid) pointer to a char on your architecture, so it is not really meaningful to represent it [the content] as a const char *.

What you may instead want is to load the contents of the file in memory, and then store a pointer (of type const char*) to the beginning of the given block. </pedantry> One way of achieving that:

#include <stringstream>
#include <fstream>
// ...
{
    std::ostringstream sstream;
    std::ifstream fs("test.txt");
    sstream << fs.rdbuf();
    const std::string str(sstream.str());
    const char* ptr = str.c_str();
    // ptr is the pointer we wanted - do note that it's only valid
    // while str is valid (i.e. not after str goes out of scope)
}