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POEfficiency of std::tuple and std::map
 

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  1. POEfficiency of std::tuple and std::map
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    <p>I am currently building a program that relies on multiple vectors and maps to retain previously computed information. My vectors are of the standard format, and not very interesting. The maps are of the form</p> <pre><code>std::map&lt;std::string, long double&gt; </code></pre> <p>with the intent of the string being a parseable mapping of one vector onto another, such as</p> <pre><code>std::map&lt;std::string, long double&gt; rmMap("fvProperty --&gt; fvTime", 3.0234); </code></pre> <p>where I can later on split the string and compare the substrings to the vector names to figure out which ones were involved in getting the number. However, I have recently found that std::tuple is available, meaning I can skip the string entirely and use the vector positions instead with</p> <pre><code>std::tuple&lt;unsigned int, unsigned int, long double&gt; </code></pre> <p>This allows me (as far as I can tell) to use both the first and the second value as a key, which seems preferable to parsing a string for my indices. </p> <p>My crux is that I am unaware of the efficiency here. There will be <em>a lot</em> of calls to these tuples/maps, and efficacy is of the essence, as the program is expected to run for weeks before producing an end result.</p> <p>Thus, I would ask you if tuples are more or equally efficient (in terms of memory, cache, and cycles) than maps when it comes to large and computationally intense programs.</p> <p>EDIT: If tuples cannot be used in this way, would the map</p> <pre><code>std::map&lt;std::pair&lt;unsigned int, unsigned int&gt;, long double&gt; </code></pre> <p>be an effective substitute to using strings for identification?</p>
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    1. COA tuple isn't a replacement for a map; it's just a simple structure with (in this case) three data members. If you want to use two values as a map key, you'll want something like `map<pair<int,int>,double>`. You may or may not find `unordered_map` to be more efficient than `map`, depending on exactly what you're doing with them.
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      1. USMike Seymour
    2. COYou will, of course, have to provide a suitable comparison function so that `map` can order things properly. Or, if you don't need an ordered map, you can use `unordered_map` and provide an appropriate hashing function.
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      1. USJoe Z
    3. CO@MikeSeymour: We typed past each other. :-) You edited your comment to say pretty much what I was adding to your comment.
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      1. USJoe Z
 

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