What is the most elegant way to read a text file with c++?


Question

I'd like to read whole content of a text file to a std::string object with c++.

With Python, I can write:

text = open("text.txt", "rt").read()

It is very simple and elegant. I hate ugly stuff, so I'd like to know - what is the most elegant way to read a text file with C++? Thanks.

1
57
11/5/2013 3:30:20 PM

Accepted Answer

There are many ways, you pick which is the most elegant for you.

Reading into char*:

ifstream file ("file.txt", ios::in|ios::binary|ios::ate);
if (file.is_open())
{
    file.seekg(0, ios::end);
    size = file.tellg();
    char *contents = new char [size];
    file.seekg (0, ios::beg);
    file.read (contents, size);
    file.close();
    //... do something with it
    delete [] contents;
}

Into std::string:

std::ifstream in("file.txt");
std::string contents((std::istreambuf_iterator<char>(in)), 
    std::istreambuf_iterator<char>());

Into vector<char>:

std::ifstream in("file.txt");
std::vector<char> contents((std::istreambuf_iterator<char>(in)),
    std::istreambuf_iterator<char>());

Into string, using stringstream:

std::ifstream in("file.txt");
std::stringstream buffer;
buffer << in.rdbuf();
std::string contents(buffer.str());

file.txt is just an example, everything works fine for binary files as well, just make sure you use ios::binary in ifstream constructor.

124
7/25/2013 5:35:54 PM

There's another thread on this subject.

My solutions from this thread (both one-liners):

The nice (see Milan's second solution):

string str((istreambuf_iterator<char>(ifs)), istreambuf_iterator<char>());

and the fast:

string str(static_cast<stringstream const&>(stringstream() << ifs.rdbuf()).str());

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