Extending std::(w)string, by adding a constructor and some member functions

Question

Sure, the std::string interface is already bloated. But it's missing some (for me) crucial elements. For example, a std::wstring cannot be constructed from a plain const char* (which is what is needed to create one from a string literal). I'd also like to add an operator/ and a split function. Anyways, that's all besides the point of the question. Which is preventing me writing a core class's guts for a project.

I know I can privately inherit from std::(w)string, and "import" all members with using. This misses the crucial non-member template functions, which are numerous.

How can I approach this better? I know public inheritance "solves" the problem, but it introduces the problems of deleteing a base class pointer of a class without a virtual destructor. Note that I'm not planning to add data members, so is this really a problem, or is this corner case still fine to use public inheritance?

Please don't say "don't do this", unless you can provide a way that 1) does what I want, 2) doesn't require me to write it all myself, 3) does not bloat my caller-side interface.

"(which is what is needed to create one from a string literal)" What about wide string literals? — dyp
– dyp, Commented Jan 3, 2014 at 21:20
To first order, std::wstring shouldn't be used at all; to second order, what's wrong with writing 'std::wstring foo(L"foo")'? Your split and operator/ (what does it even mean to divide strings?!) can perfectly well be free functions, can't they? — zwol
– zwol, Commented Jan 3, 2014 at 21:23
@DyP: I don't care about those. Just plain text string literals in any place you'd normally use them. I want to use wstring on Windows and string everywhere else, but I want to use standard interfaces, so no special tcout and tchar. It's very much possible, there's enough typedefs to hide the underlying type's real name. — rubenvb
– rubenvb, Commented Jan 3, 2014 at 21:23
You should instead use string (containing UTF-8) everywhere including Windows, converting to "wide"ness only to pass directly to or from Win32 API functions that require it. — zwol
– zwol, Commented Jan 3, 2014 at 21:25
@rubenvb: That's not gonna happen (and really the wrong approach). You need to pick one encoding, like UTF-8 or UTF-16, and use it everywhere on all platforms, and then convert in/out of OS APIs on the platforms where they don't match. The existing design simply doesn't really support what you want to do. — Puppy
– Puppy, Commented Jan 3, 2014 at 21:25

Dietmar Kühl · Accepted Answer · 2014-01-03 21:22:45Z

11

Do not derive from std::basic_string<...> but rather create algorithms doing the appropriate operations, e.g.:

template <typename cT>
std::basic_string<cT> construct(char const* str) {
    // ...
}

Likewise for split(), operator/(), etc. In principle, most members of std::basic_string<...> shouldn't be members in the first place...

answered Jan 3, 2014 at 21:22

Dietmar Kühl

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3 Comments

rubenvb Over a year ago

I stress that I do not want to bloat my caller-side interface. This is terrible in that respect. I agree it's better design-wise, but it'll produce a lot of wrapper code... I added this as point 3.

Dietmar Kühl Over a year ago

@rubenvb: I disagree. Member functions for anything but non-crucial object maintenance is plain wrong.

zwol Over a year ago

I don't understand why free functions of the form vector<string> split(string const& text, const char *separator) would "bloat your caller-side interface" any more than hypothetical new string members would. You've already been told what to do about constructing wstring from const char * (i.e. "don't").

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