std::stringstream question

What is the easiest way to tell if an extraction from a stringstream parsed all the stream, or only part of it?

E.g. I want to use this for, say, string -> int conversion. If I have an input, "-123", then it should parse the entire string and return -123. If I have the input "-123abc", it also returns "-123" but I want to make this an error condition (as the input string was not a properly formatted int) rather than silently parsing only half of the input string and returning.

The reason I am using stringstream is firstly as I rarely use it and want the practice, secondly because I can easily make this a function template and be able to extract any kind of data that std::stringstream can work with.

If I understood your question, one way would be to have a templated class that would both do the parsing and store the results. I'm not comfortable around templates yet. So, instead of showing you the actual class skeleton (which you can probably do better than me), maybe show you its use...

Code:

---

istringstream myText;

/*...*/

strParse<int> result(myText);

result.value();  // outputs value
result.error();  // probably returns an int
result.desc();  // error description

---

Or if you are going to work with just one datatype, ignore the template

I think I solved it, the following is my code:

Code:

---

template <typename Type>
        Type FromString(tstring str){
               
                Type t;
                std::basic_stringstream<TCHAR> s(str);
                s >> t;

                if ((int) s.tellg() != (int) str.size())
                        throw std::runtime_error("Extraction Failed");
                return t;
        }

---

Basically I am checking if the number of bytes parsed is different from the length of the input string.


I think your way should work, too, Mario. I may recode this as a templated class instead of a templated function.

Ok... I hadn't understood your question. Now I do :)

Also consider this:
http://www.parashift.com/c++-faq-lit....html#faq-39.2

Code:

---

template<class T>
bool parse(T &e, const std::string &s) {
    std::istringstream iss(s);
    return (iss >> e) && iss.eof();
// or, to accept trailing whitespace
    return (iss >> e >> std::ws) && iss.eof();
}

---

you can look to boost::lexical_cast for a more thourough example.