Usage of HashTable in C,

Usage of HashTable in C,

1. Brief description of the hash table (Hashtable)

In. in the. NET Framework, Hashtable is System. A container provided by the Collections namespace is used to process and present key-value pairs similar to the keyvalue. The key is usually used for quick search, and the key is case sensitive; value is used to store the value corresponding to the key. In Hashtable, keyvalue pairs are of the object type, so Hashtable can support any type of keyvalue pairs.

Ii. Simple operations on Hash Tables

Add a keyvalue key-value pair in the hash table: HashtableObject. Add (key, value );
Remove a keyvalue key-value pair in the hash table: HashtableObject. Remove (key );
Remove all elements from the hash table: HashtableObject. Clear ();
Determine whether the hash table Contains the specified key: HashtableObject. Contains (key );
The following console contains all the preceding operations:
Using System;
Using System. Collections; // This namespace must be introduced when Hashtable is used.
Class hashtable
{
Public static void Main ()
{
Hashtable ht = new Hashtable (); // create a Hashtable instance
Ht. Add ("E", "e"); // Add a keyvalue pair
Ht. Add ("A", "");
Ht. Add ("C", "c ");
Ht. Add ("B", "B ");

String s = (string) ht ["A"];
If (ht. Contains ("E") // checks whether the hash table Contains a specific key. The return value is true or false.
Console. WriteLine ("the E key exist ");
Ht. Remove ("C"); // Remove a keyvalue
Console. WriteLine (ht ["A"]); // output
Ht. Clear (); // remove all elements
Console. WriteLine (ht ["A"]); // there will be no output here
}
}

3. traverse the hash table

DictionaryEntry Object is required to traverse a hash table. The Code is as follows:
For (KeyValuePair de in ht) // ht is a Hashtable instance.
{
Console. WriteLine (de. Key); // de. Key corresponds to the key
Console. WriteLine (de. Value); // de. Key corresponds to the Key-value Pair
}

4. Sort hash tables

The definition of sorting hash tables here is to re-arrange the keys in the key-Value Pair according to certain rules, but in fact this definition cannot be implemented, because we cannot re-arrange keys directly in Hashtable, if Hashtable needs to provide output of certain rules, we can adopt a work und:
ArrayList akeys = new ArrayList (ht. Keys); // do not forget to import System. Collections
Akeys. Sort (); // Sort by letter
For (string skey in akeys)
{
Console. Write (skey + ":");
Console. WriteLine (ht [skey]); output after sorting
}