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Asked: 2026-05-11T18:06:40+00:00

basically i have (state, state code) pairs, that are subsets of country [USA] ->

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basically i have (state, state code) pairs, that are subsets of country
[USA] -> [VT] -> 32

so i’m using std::map<tstring<std::map<tstring, unsigned int>> but i’m having trouble with assignment of the state code

for(std::map<tstring, std::map<tstring, unsigned int>>::const_iterator it = countrylist.begin(); it != countrylist.end(); ++it) 
{
foundCountry = !it->first.compare(_T("USA")); //find USA 
if(foundCountry) it->second[_T("MN")] = 5; //Assignment fails
}

error C2678: binary '[' : no operator found which takes a left-hand operand of type 'const std::map<_Kty,_Ty>'

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1 Answer

  1. Editorial Team

    operator[] on std::map is non-const, because it creates the entry if it doesn’t already exist. So you can’t use a const_iterator in this way. You can use find() on const maps, but that still won’t let you modify their values.

    And Smashery is right, you’re doing the first lookup in a strange way considering that you have a map. Since you’re clearly modifying the thing, what’s wrong with this?

    countryList[_T("USA")][_T("MN")] = 5;
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