fstream to const char *

问题

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?

回答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

回答2:

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 <sstream>
#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)
}

回答3:

You need to:

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

来源：https://stackoverflow.com/questions/4010207/fstream-to-const-char

标签

c++

fstream