Why doesn't C++ reimplement C standard functions with C++ elements/style?

Question

For a specific example, consider atoi(const std::string &). This is very frustrating, since we as programmers would need to use it so much.

Answer 1

The tongue in cheek answer is: Because STL is a half-hearted attempt to show how powerful C++ templates could be. Before they got to each corner of the problem space, time was up.

There are two reasons: Creating an API takes time and effort. Create a good API takes a lot of time and a huge effort. Creating a great API takes an insane amount of time and an incredible effort. When the STL was created, OO was still pretty new to the C++ people. They didn't have the ideas how to make fluent and simple API. Today, we think iterators are so 1990 but at the time, people thought "Bloody hell, why would I need that? for (int i=0; i<...) has been good enough for three decades!"

So STL didn't became the great, fluent API. This isn't all C++ fault because you can make good APIs with C++. But it was the first attempt to do that and it shows. Before the API could mature, it was turned into a standard and all the ugly shortcomings were set into stone. And on top of this, there was all this legacy code and all the libraries which already could do everything, so the pressure wasn't really there.

To solve your misery, give up on STL and have a look at the successors: Try boost and maybe Qt. Yeah, Qt is a UI library but it also has a pretty good standard library.

Answer 2

For your example, you've got two options:

std::string mystring("4");
int myint = atoi(mystring.c_str());

Or something like:

std::string mystring("4");
std::istringstream buffer(mystring);
int myint = 0;
buffer >> myint;

The second option gives you better error management than the first.

Answer 3

There's no good way to know if atoi fails. It always returns an integer. Is that integer a valid conversion? Or is the 0 or -1 or whatever indicating an error? Yes it could throw an exception, but that would change the original contract, and you'd have to update all your code to catch the exception (which is what the OP is complaining about).

If translation is too time consuming, write your own atoi:

int atoi(const std::string& str)
{
    std::istringstream stream(str);
    int ret = 0;
    stream >> ret;
    return ret;
}

Answer 4

You can write a more generic string to number convert as such:

template <class T>
T strToNum(const std::string &inputString,
           std::ios_base &(*f)(std::ios_base&) = std::dec)
{
    T t;
    std::istringstream stringStream(inputString);

    if ((stringStream >> f >> t).fail())
    {
        throw runtime_error("Invalid conversion");
    }
    return t;
}


// Example usage
unsigned long ulongValue = strToNum<unsigned long>(strValue);
int intValue             = strToNum<int>(strValue);

int intValueFromHex      = strToNum<int>(strHexValue,std::hex);
unsigned long ulOctValue = strToNum<unsigned long>(strOctVal, std::oct);