Convert std::ostream to std::string

Question

Legacy code I maintain collects text into an std::ostream. I'd like to convert this to a std::string.

I've found examples of converting std::sstringstream, std::ostringstream etc to std::string but not explicitly std::ostream to std::string.

How can I do that? (Ancient C++ 98 only, no boost please)

Answer 1

• If you have a a stringstream or a ostreamstring, object or reference, just use the ostringstream::str() method that does exactly what you want: extract a string. But you know that and you apparently have a ostream object, not a stringstream nor a ostreamstring.

• If your ostream reference is actually a ostringstream or a stringstream, use ostream::rdbuf to get a streambuf, then use this post to see how to extract a string.

Example:

#include <iostream>
#include <sstream>

std::string toString( std::ostream& str )
{
    std::ostringstream ss;
    ss << str.rdbuf();
    return ss.str();
}

int main() {

    std::stringstream str;
    str << "Hello";

    std::string converted = toString( str );

    std::cout << converted;

    return 0;
}

Live demo: http://cpp.sh/6z6c

• Finally, as commented by M.M, if your ostream is a ofstream or an iostream, most likely it clears its buffer so you may not be able to extract the full content as proposed above.

Answer 2

Try this

 std::ostringstream stream;
 stream << "Some Text";
 std::string str =  stream.str();