Is it normal practice or very bad to nest maps?

Is it normal practice or very bad to nest maps several levels?

        // name property     // name singal         // interval of Ranges      // values

typedef std::map<std::string, std::map<std::string, std::map<RangeSignalValue, std::string > > > sgHashSi开发者_运维知识库gnals;

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I've certainly done this. However, I'd break down the definition into digestible chunks:

typedef std::map<RangeSignalValue, std::string> RangeIntervalMap; 
typedef std::map<std::string, RangeIntervalMap> NameSignalMap;
typedef std::map<std::string, NameSignalMap>    NamePropertyMap;

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If it makes sense in the context you're working in then I don't see any problems, other than it might be hard to read. Might it be possible to use typedef to make some of these nested maps easier to understand?

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For instance:

typedef std::map<RangeSignalValue, std::string> RangesValues;

typedef std::map<std::string, std::map<std::string, RangesValues > > sgHashSignals;

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The biggest issue is that lookup is slightly slower than the alternative:

           // property+signal, concatenated // interval of Ranges    // values

typedef std::map<std::string, std::map<RangeSignalValue, std::string > > sgHashSignals;

Precisely how you should concatenate the first two strings depends on their syntax, though.

This replaces two string lookups by one. The downside is that it takes more memory.