Loading a file into a vector<char>

I woul开发者_如何学Pythond like to load the contents of a text file into a vector<char> (or into any char input iterator, if that is possible). Currently my code looks like this:

std::vector<char> vec;
std::ifstream file("test.txt");
assert(file.is_open());
while (!(file.eof() || file.fail())) {
    char buffer[100];
    file.read(buffer, 100);
    vec.insert(vec.end(), buffer, buffer + file.gcount());
}

I do not like the manual use of a buffer (Why 100 chars? Why not 200, or 25 or whatever?), or the large number of lines that this took. The code just seems very ugly and non-C++. Is there a more direct way of doing this?

---

If you want to avoid reading char by char:

if (!file.eof() && !file.fail())
{
    file.seekg(0, std::ios_base::end);
    std::streampos fileSize = file.tellg();
    vec.resize(fileSize);

    file.seekg(0, std::ios_base::beg);
    file.read(&vec[0], fileSize);
}

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I think it's something like this, but have no environment to test it:

std::copy(std::istream_iterator<char>(file), std::istream_iterator<char>(), std::back_inserter(vec));

Could be you have to play with io manipulators for things like linebreaks/whitespace.

Edit: as noted in comments, could be a performance hit.

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Another approach, using rdbuf() to read the whole file to a std::stringstream first:

#include <fstream>
#include <sstream>
#include <vector>
#include <string>

// for check:
#include <algorithm>
#include <iterator>
#include <iostream>

int main() {
   std::ifstream file("test.cc");
   std::ostringstream ss;
   ss << file.rdbuf();
   const std::string& s = ss.str();
   std::vector<char> vec(s.begin(), s.end());

   // check:
   std::copy(vec.begin(), vec.end(), std::ostream_iterator<char>(std::cout));
}

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There were lots of good responses. Thanks all! The code that I have decided on using is this:

std::vector<char> vec;
std::ifstream file;
file.exceptions(
    std::ifstream::badbit
  | std::ifstream::failbit
  | std::ifstream::eofbit);
//Need to use binary mode; otherwise CRLF line endings count as 2 for
//`length` calculation but only 1 for `file.read` (on some platforms),
//and we get undefined  behaviour when trying to read `length` characters.
file.open("test.txt", std::ifstream::in | std::ifstream::binary);
file.seekg(0, std::ios::end);
std::streampos length(file.tellg());
if (length) {
    file.seekg(0, std::ios::beg);
    vec.resize(static_cast<std::size_t>(length));
    file.read(&vec.front(), static_cast<std::size_t>(length));
}

Obviously, this is not suitable for extremely large files or performance-critical code, but it is good enough for general purpose use.

---

use an iterator:

#include <iterator>

istream_iterator<char> data( file );
istream_iterator<char> end;
vec.insert( std::back_inserter(vec), data, end );