map<int,int> default values

c++ dictionary default
Bill Kotsias picture Bill Kotsias · Apr 19, 2010 · Viewed 52.7k times · Source 
std::map<int,int> mapy;
++mapy[5];

Is it safe to assume that mapy[5] will always be 1? I mean, will mapy[5] always get the default value of 0 before '++', even if not explicitly declared, as in my code?

Answer

rep_movsd picture rep_movsd · Apr 19, 2010

As soon as you access the map with the [] operator, if the key doesn't exist it gets added. The default initializer of the int type gets invoked - so it will get a value of 0.

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