C Java HashMap equivalent

Question

Coming from a Java world into a C  one is there a HashMap equivalent  If not what would you recommend

User · Answer

the answer is

Dictionary

take look at my function, its simple add uses most important member functions inside Dictionary

this function return false if the list contain Duplicates items

 public static bool HasDuplicates<T>(IList<T> items)
    {
        Dictionary<T, bool> mp = new Dictionary<T, bool>();
        for (int i = 0; i < items.Count; i++)
        {
            if (mp.ContainsKey(items[i]))
            {
                return true; // has duplicates
            }
            mp.Add(items[i], true);
        }
        return false; // no duplicates
    }

User · Answer

Dictionary is probably the closest  System Collections Generic Dictionary implements the System Collections Generic IDictionary interface  which is similar to Java s Map interface    Some notable differences that you should be aware of    Adding Getting items   Java s HashMap has the put and get methods for setting getting items   myMap put key  value  MyObject value   myMap get key   C  s Dictionary uses    indexing for setting getting items   myDictionary key    value MyObject value   myDictionary key    null keys   Java s HashMap allows null keys  NET s Dictionary throws an ArgumentNullException if you try to add a null key  Adding a duplicate key   Java s HashMap will replace the existing value with the new one   NET s Dictionary will replace the existing value with the new one if you use    indexing   If you use the Add method  it will instead throw an ArgumentException   Attempting to get a non-existent key   Java s HashMap will return null   NET s Dictionary will throw a KeyNotFoundException   You can use the TryGetValue method instead of the    indexing to avoid this  MyObject value   null  if   myDictionary TryGetValue key  out value        key doesn t exist         Dictionary s has a ContainsKey method that can help deal with the previous two problems

User · Answer

Check out the documentation on MSDN for the Hashtable class       Represents a collection of key-and-value pairs that are organized based on the hash code of the key     Also  keep in mind that this is not thread-safe

User · Answer

I just wanted to give my two cents  This is according to  Powerlord  s answer   Puts  null  instead of null strings   private static Dictionary lt string  string gt  map   new Dictionary lt string  string gt      public static void put string key  string value        if  value    null  value    null       map key    value     public static string get string key  string defaultValue        try               return map key             catch  KeyNotFoundException e                return defaultValue           public static string get string key        return get key   null

User · Answer

From C  equivalent to Java HashMap  I needed a Dictionary which accepted a  null  key  but there seems to be no native one  so I have written my own  It s very simple  actually  I inherited from Dictionary  added a private field to hold the value for the  null  key  then overwritten the indexer  It goes like this    public class NullableDictionnary   Dictionary lt string  string gt        string null value       public StringDictionary this string key                get                       if  key    null                                 return null value                            return base key                     set                       if  key    null                                null value   value                            else                                base key    value                                    Hope this helps someone in the future               I modified it to this format  public class NullableDictionnary   Dictionary lt string  object gt

User · Answer

Use Dictionary - it uses hashtable but is typesafe   Also  your Java code for   int a   map get key     continue with your logic   will be best coded in C  this way   int a  if dict TryGetValue key  out a      continue with your logic     This way  you can scope the need of variable  a  inside a block and it is still accessible outside the block if you need it later

User · Answer

Let me help you understand it with an example of  codaddict s algorithm    Dictionary in C   is  Hashmap in Java  in parallel universe   Some implementations are different  See the example below to understand better   Declaring Java HashMap   Map lt Integer  Integer gt  pairs   new HashMap lt Integer  Integer gt       Declaring C  Dictionary   Dictionary lt int  int gt  Pairs   new Dictionary lt int  int gt       Getting a value from a location   pairs get input i       in Java Pairs input i           in C    Setting a value at location   pairs put k - input i   input i       in Java Pairs k - input i     input i         in C    An Overall Example can be observed from below Codaddict s algorithm   codaddict s algorithm in Java   import java util HashMap   public class ArrayPairSum        public static void printSumPairs int   input  int k                Map lt Integer  Integer gt  pairs   new HashMap lt Integer  Integer gt              for  int i   0  i  lt  input length  i                          if  pairs containsKey input i                    System out println input i           pairs get input i                 else                 pairs put k - input i   input i                          public static void main String   args                int   a     2  45  7  3  5  1  8  9            printSumPairs a  10              Codaddict s algorithm in C   using System  using System Collections Generic   class Program       static void checkPairs int   input  int k                Dictionary lt int  int gt  Pairs   new Dictionary lt int  int gt              for  int i   0  i  lt  input Length  i                          if  Pairs ContainsKey input i                                  Console WriteLine input i           Pairs input i                               else                               Pairs k - input i     input i                                     static void Main string   args                int   a     2  45  7  3  5  1  8  9              method   codaddict s algorithm   O n          checkPairs a  10           Console Read

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