CODEWITHSUNDEEP
c++stliterator
ExOttoyuhr
ExOttoyuhr

Reputation: 677

(C++) Finding end() for an iterator when only the iterator is available?

Assuming code that looks vaguely like this:

bool LoadGame() {
  vector<string> SaveFile = LoadFromSaveFile();
  Data = SaveFile.begin();
  LoadCharacters(&Data);
    // containing LoadOneCharacter(&Data) calls
  LoadLocations(&Data);
    // >> LoadOneLocation(&Data) calls
  // etc.
}

Is there any way to check whether Data is currently pointing at SaveFile::end() while within LoadCharacters(), LoadLocations(), etc., without passing SaveFile::end() to all the functions invoked by LoadGame()?

(If only dereferencing end() and beyond threw an exception instead of generating undefined behavior!)

Upvotes: 3

Views: 203

Answers (2)

sehe
sehe

Reputation: 392911

This is not possible, in the general case

In specific cases, you may be able to exploit implementation specific details of the iterator implementation to get at the container.

The iterators of the standard container library have no such details documented AFAIR.

A special case would be input iterators like std::istream_iterator<> which can always be compared to default-constructed instance of itself to check for end-of-input.

std::istringstream iss("test");
std::istream_iterator<char> it(iss);

// you can always check for end of input:
while (std::istream_iterator<char>() != it)
{
    it++;
}

Upvotes: 5

Michael Anderson
Michael Anderson

Reputation: 73480

It's not possible in general. In many implementations many kinds of iterators are just pointers, and have no understanding of the underlying container.

You'll need to pass both iterators, or pass a different structure such as a range ( which is in boost but not C++0x IIRC).

Upvotes: 5

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