Improve company productivity with a Business Account.Sign Up

x
?
Solved

insert and incompatible iterators

Posted on 2013-12-31
1
Medium Priority
?
412 Views
Last Modified: 2014-01-13
As an exercise, I am implementing my own versions of the STL containers std::vector and std::string. When implementing my version of the following insert method

 void insert (iterator position, InputIterator first, InputIterator last);

Open in new window

I would like to check that the input iterators first and last refer to the same container. I know that the STL containers carry out such a check, since if one tries to use insert when this condition fails, one gets an error, e.g., "string iterators incompatible". How is this check implemented for STL containers?
0
Comment
Question by:Rothbard
1 Comment
 
LVL 35

Accepted Solution

by:
sarabande earned 1600 total points
ID: 39751800
with my compiler (ms visual c++ 2008) the following compiles without error:

std::vector<std::string> v0, v1, v2;

v0.push_back("ABC");
v1.push_back("DEF");
v2.push_back("GHI");
v0.insert(v0.begin(), v1.begin(), v2.end());

Open in new window


even if I exchange the 2nd and 3rd argument there is no (compiler) error.

however at runtime there is a check if you run the code in the debugger. the debugger has additional information for arguments at runtime and "knows" to which container an iterator belongs. because of that it would find out that v2.end() is beyond the range spanned by v1.begin() and v1.end() and therefore I get a debug assertion.

at my system it happened in function std::vector::const_iterator::operator== member function.

#if _HAS_ITERATOR_DEBUGGING
     Compat(_Right);
#else
     _SCL_SECURE_VALIDATE(this->_Has_container() && this->_Same_container(_Right));
#endif /* _HAS_ITERATOR_DEBUGGING */

Open in new window


when calling the Compat member function.

the operator == compares the right boundaries of the containers defined by the iterators first and last. it is checked in debug mode by calling the global function _Debug_range which exactly does the check you talked of.

void __CLRCALL_OR_CDECL _Debug_range(_InIt _First, _InIt _Last, const wchar_t *_File, unsigned int _Line)
{   // test iterator pair for valid range
    ...
}

Open in new window


in release mode the program crashes because of the error. when I run it from IDE it breaks in the function _Distance(_First, _Last, _Count); with access violation what is not very surprising because the (pointer) addresses associated with the iterators would not span a useable array of strings especially if using string class objects.

Sara
0

Featured Post

Keep up with what's happening at Experts Exchange!

Sign up to receive Decoded, a new monthly digest with product updates, feature release info, continuing education opportunities, and more.

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

This article will show you some of the more useful Standard Template Library (STL) algorithms through the use of working examples.  You will learn about how these algorithms fit into the STL architecture, how they work with STL containers, and why t…
Container Orchestration platforms empower organizations to scale their apps at an exceptional rate. This is the reason numerous innovation-driven companies are moving apps to an appropriated datacenter wide platform that empowers them to scale at a …
The viewer will learn how to user default arguments when defining functions. This method of defining functions will be contrasted with the non-default-argument of defining functions.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

608 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question