C equivalent of C map string double

Question

I want to keep some totals for different accounts  In C   I d use STL like this   map lt string double gt  accounts      Add some amounts to some accounts  accounts  Fred      4 56  accounts  George      1 00  accounts  Fred      1 00   cout  lt  lt   Fred owes me     lt  lt  accounts  Fred    lt  lt  endl    Now  how would I do the same thing in C

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This code is all you need      static void Main string   args            String xml                   lt transactions gt                   lt transaction name   Fred   amount   5 20     gt                   lt transaction name   John   amount   10 00     gt                   lt transaction name   Fred   amount   3 00     gt               lt  transactions gt             XDocument xmlDocument   XDocument Parse xml            var query   from x in xmlDocument Descendants  transaction                       group x by x Attribute  name   Value into g                     select new   Name   g Key  Amount   g Sum t   gt  Decimal Parse t Attribute  amount   Value               foreach  var item in query                Console WriteLine  Name   0   Amount   1 C     item Name  item Amount                     And the content is   Name  Fred  Amount  R  8 20   Name  John  Amount  R  10 00   That is the way of doing this in C  - in a declarative way   I hope this helps    Ricardo Lacerda Castelo Branco

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Dictionary lt string  double gt  accounts

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You want the Dictionary class

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While we are talking about STL  maps and dictionary  I d recommend taking a look at the C5 library   It offers several types of dictionaries and maps that I ve frequently found useful  along with many other interesting and useful data structures      If you are a C   programmer moving to C  as I did  you ll find this library a great resource  and a data structure for this  dictionary    -Paul

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Roughly -  var accounts   new Dictionary lt string  double gt         Initialise to zero     accounts  Fred     0  accounts  George     0  accounts  Fred     0      Add cash  accounts  Fred      4 56  accounts  George      1 00  accounts  Fred      1 00   Console WriteLine  Fred owes me   0    accounts  Fred

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Although System Collections Generic Dictionary matches the tag  hashmap  and will work well in your example  it is not an exact equivalent of C   s std  map - std  map is an ordered collection   If ordering is important you should use SortedDictionary

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The closest equivalent of C   std  map lt  gt   a tree internally  is C  OrderedDictionary lt  gt   a tree internally   while C  OrderedDictionary lt  gt  is missing some very important methods from C   std  map lt  gt   namely  std  map  find  std  map  lower bound  std  map  upper bound  std  map  equal range  and std  map iterators  which are basically the backbone for the previous 4 methods   Why those 4 methods are important  Because it gives us the ability to locate the  whereabouts  of a given key  in addition to only being able to check if a key exists  or the SortedDictionary is guaranteed to be ordered   What is  whereabouts  of a key in a std  map  The key doesn t necessarily have to exist in the collection  we want to know the location the key might be at  usually between two iterators pointing to two adjacent existing keys respectively in the collection  so we can operate on the range the key falls into in a O logN  complexity  Without such 4 methods  with iterators   one has to do an O N  iteration through the collection every time a range is queried against a key

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Dictionary is the most common  but you can use other types of collections  e g   System Collections Generic SynchronizedKeyedCollection  System Collections Hashtable  or any KeyValuePair collection

[c#] C# equivalent of C++ map<string,double>

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