errors with multimap (key type is std::string)

Question

I've been having problems with getting multimap to work. I'll just show the code and describe the problem:

 #include <string> ... multimap<std::string, pinDelayElement> arcList pinDelayElement pde; std:string mystring = "test" arcList[mystring] = pde;

However, when I compile, the last line gives me the following error:

error C2676: binary '[' : 'std::multimap<_Kty,_Ty>' does not define this operator or a conversion to a type acceptable to the predefined operator with [ _Kty=std::string, _Ty=Psdfwr::pinDelayElement ]

Does anyone know something I might be doing wrong?

ok, I've tried it before (and just tried it again) with std::string mystring = "test"; arcList[mystring] = pde; and it gives me the same error, so, changing that doesn't fix it — Cameron R
– Cameron R, Commented Jun 21, 2012 at 20:46
@Cameron R: Then update your code and compiler error accordingly. — K-ballo
– K-ballo, Commented Jun 21, 2012 at 20:48

juanchopanza · Accepted Answer · 2012-06-21 20:49:36Z

6

That is because std::multimap doesn't have an operator[]. Try using the insert method.

answered Jun 21, 2012 at 20:49

juanchopanza

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Cameron R Over a year ago

Ah, that makes sense. I had something similar working with map which is why this was confusing for me. I guess it makes sense that it wouldn't be so easy to index with just the key for a multimap. Thanks!

Kuba hasn't forgotten Monica · Accepted Answer · 2012-06-21 20:53:15Z

The code below is an example of how to do it properly.

As others pointed out, std::multimap doesn't have the indexing operator[] because it makes no sense to extract elements out of it -- there are multiple values per each index.
You must insert a multimap<...>::value_type.

#include <string> #include <map> void test() { typedef std::multimap<std::string, int> Map; Map map; map.insert(Map::value_type("test", 1)); }

Thanks a lot. Yeah, it occurred to me after reading juanchopanza's comment that it wouldn't make sense to extract by index the way I was trying to

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