STL map (read only)

[hectorDUQUE]

hi guys,

do you know what this means:

error: increment of data-member 'std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>::second' in read-only structure

i don't understand how a map structure can be a read only structure. The code is:

          typedef std::map<string, int> map_groups2counters_type;

	  map_groups2counters_type::const_iterator groups2countersIterator;
	  groups2countersIterator = groups2counters.find( groups2counters_mapKey_ch );

	  if ( groups2countersIterator == groups2counters.end() ){

	    //does not exist, so initializa the counter
	    groups2counters.insert(std::make_pair(groups2counters_mapKey_ch, 1));

	  } else{

	    //exists, so increase the counter
	    groups2countersIterator->second++;

	  }//if

thanks in advance,

hector

 

[hectorDUQUE]

the error was reported in the line

         groups2countersIterator->second++;

 

[Salem]

Perhaps this?
[tt]map_groups2counters_type::[red]const_[/red]iterator[/tt]
shouldn't be const if you intend to modify things.



--
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.

 

[hectorDUQUE]

yes, it is!

but, i don´ t understantd why. It is not the iterator it self which i ám trying to modify.

????

thanks ....

hector

 

[cpjust]

A const_iterator means the thing the iterator is pointing to is const, not the iterator (otherwise, how could you iterate in the first place?)