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c++; map interator; detecting when a find() returns an invalid iterator

Posted on 2008-10-14
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Last Modified: 2012-05-05
I've got a map<string,string> as part of a class and am writing a function to delete one of the map items, based on the key name. Once I obtain the iterator - through a find() - I tell it to erase it from the map.  Works great if it finds a match.  If it doesn't find a match, VS2005 pops up an errors "debug assertion failed!".  

I've looked online and cannot find anything which dictates how to test an iterator for a NULL/invalid value.  I finally discovered a solution which IMHO seems rather clunky... but it does the job.

if(iter._Ptr->_Isnil) { return; } //  exit method if invalid iterator

I find it difficult to believe this is the proper way to test for an invalid iterator.  Is there a better way?  The full 'delete' method is listed below.

Oh and I suppose I should mention, this is a cross-platform app, so g++ 4.1.2 will also need to be able to compile it.
void deleteItem(string key) {

    map<string,string>::iterator i = this->_Items->find(key);

    if(i._Ptr->_Isnil) { return; }

    this->_Items->erase(i);

  }

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Question by:BaconU
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Accepted Solution

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LordOfPorts earned 75 total points
ID: 22713200
If find does not detect value it should return map::end http://www.cplusplus.com/reference/stl/map/find.html
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Expert Comment

by:wktang83
ID: 22713289

void deleteItem(string key) {

    map<string,string>::iterator i = this->_Items->find(key);

    if(i._Ptr == this->_Items->end()) { return; }

    this->_Items->erase(i);

  }

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Author Closing Comment

by:BaconU
ID: 31505968
Ah, yes... I should have known.  I mistakenly assumed that the end() was only to be used in conjunction with begin().  

This is a much nicer solution!  Thanks LordOfPorts!
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Author Comment

by:BaconU
ID: 22713868
wktang83, according to my tests, you don't need the ._Ptr when testing again end().
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