Question

I’m trying to read an ifstream into a string, where I can set the number of characters being read. I’ve read the documentation for ifstream.get() and ifstream.getline(), but neither of those accomplish what I want.

Given the following string:

asdfghjklqwertyuiop

I want to read in varying number of characters at a time into a string. I’ve started like this, but I’m getting an error that there’s no function that will take a string as the first parameter:

string destination;
int numberOfLettersToGet = 1;

while (inputstream.get(destination, numberOfLettersToGet)){
   //Do something.
}

What can I use instead of inputstream.get()?

Answer 1

You may like to use read and gcount member-functions of std::istream. get appends a zero-terminator, which is unnecessary when you read into std::string.

std::string destination;
int numberOfLettersToGet = 1;

destination.resize(numberOfLettersToGet);
std::streamsize n = inputstream.gcount();
inputstream.read(&destination[0], numberOfLettersToGet);
destination.resize(inputstream.gcount() - n); // handle partial read