C# Dictionary, Read and Write Binary File

Store a Dictionary in a binary file using BinaryWriter and BinaryReader.

Dictionary, binary file. A Dictionary can be stored in a binary file. This provides excellent performance. By combining FileStream, BinaryReader and BinaryWriter, we develop here a custom file format that allows for efficient persistence of a Dictionary.BinaryWriter BinaryReader

Example. First we mention the file format. The binary file where the Dictionary is persisted contains a single 32-bit integer at the start. This tells us how many pairs are found in the rest of the file. Then, we simply can read in that many pairs.

Main: Here you are asked to either Write the Dictionary and its contents to the file, or Read in a Dictionary from that file.

Console.ReadLine

Write: In Write, we use the using statement on a FileStream and BinaryWriter. We implement the simple file format described.

Read: In Read, we use a FileStream and BinaryReader and then loop through the required number of pairs.

C# program that reads and writes binary file for Dictionary using System; using System.Collections.Generic; using System.IO; class Program { static void Main() { while (true) { Console.WriteLine("1=Write, 2=Read"); string value = Console.ReadLine(); if (value == "1") { var dictionary = new Dictionary<string, string>(); dictionary["Codex"] = "dot"; dictionary["net"] = "Codex"; dictionary["dot"] = "net"; Write(dictionary, "C:\\dictionary.bin"); } else if (value == "2") { var dictionary = Read("C:\\dictionary.bin"); foreach (var pair in dictionary) { Console.WriteLine(pair); } } } } static void Write(Dictionary<string, string> dictionary, string file) { using (FileStream fs = File.OpenWrite(file)) using (BinaryWriter writer = new BinaryWriter(fs)) { // Put count. writer.Write(dictionary.Count); // Write pairs. foreach (var pair in dictionary) { writer.Write(pair.Key); writer.Write(pair.Value); } } } static Dictionary<string, string> Read(string file) { var result = new Dictionary<string, string>(); using (FileStream fs = File.OpenRead(file)) using (BinaryReader reader = new BinaryReader(fs)) { // Get count. int count = reader.ReadInt32(); // Read in all pairs. for (int i = 0; i < count; i++) { string key = reader.ReadString(); string value = reader.ReadString(); result[key] = value; } } return result; } } Output 1=Write, 2=Read 1 1=Write, 2=Read 2 [Codex, dot] [net, Codex] [dot, net] 1=Write, 2=Read

You can see the Dictionary was written to the file. The Dictionary instances are separate in Main. I checked the C:\dictionary.bin file that was used. The file was 32 bytes, which means the characters were encoded with one byte each.

Discussion. There are many advantages to using a custom binary format to persist a collection such as a Dictionary. For one, if you are using integers instead of strings, a binary format can be used to efficiently encode these.

Also: Performance reading in the file is good. It doesn't require much parsing. The reads are sequential and thus exploit the cache.

The above code is efficient. But it could be faster. In the Read method, you could use the count integer read in from the file as the capacity in the Dictionary constructor. This eliminates resizes to the Dictionary's structures.Capacity Dictionary

Note: Thanks to Paul Bright for suggesting an article that shows how to read and write a Dictionary to a binary file.

Summary. A Dictionary can be written to and read from a binary file. This can improve performance dramatically in some cases. We developed a simple file format that stores the number of pairs in the first integer in the binary file.

And: This solution could be adapted to more complex Dictionary types and optimized further.

The Dev Codes

.Net

.NET Array Dictionary List String 2D Async DataTable Dates DateTime Enum File For Foreach Format IEnumerable If IndexOf Lambda LINQ Parse Path Process Property Regex Replace Sort Split Static StringBuilder Substring Switch Tuple

Java

Core Array ArrayList HashMap String 2D Cast Character Console Deque Duplicates File For Format HashSet If IndexOf Lambda Math ParseInt Process Random Regex Replace Sort Split StringBuilder Substring Switch Vector While

TheDeveloperBlog.com

C# Dictionary, Read and Write Binary File

Related Links:

.Net

Java

Related Links