Question

How do I go about using the constructor for a member which is a string? Here is an example (which is wrong I realize)

class Filestring {
public:
    string      sFile;

    Filestring(const string &path)
    {
        ifstream filestream(path.c_str());
        // How can I use the constructor for the member sFile??
        // I know this is wrong, but this illustrates what I want to do.
        string sFile((istreambuf_iterator<char>(filestream)), istreambuf_iterator<char>());
    }
};

So basically I want to be able to use the member sFile’s constructor without doing a string copy. Is there a way to achieve this through assignment?

Answer 1

The best you can use is string::assign:

sFile.assign(istreambuf_iterator<char>(filestream), istreambuf_iterator<char>());

But in C++11 there is a move assignment operator for string so doing the following is almost as efficient (there is no copy of character data, the character data are moved):

sFile = string(istreambuf_iterator<char>(filestream), istreambuf_iterator<char>());

Yet another trick when C++11 move assignment is not avaliable is to use std::swap or string::swap. The efficiency would be probably almost identical to the move assignment variant.

string newContent(istreambuf_iterator<char>(filestream), istreambuf_iterator<char>());
std::swap(sFile, newContent); // or sFile.swap(newContent);