C# String Between, Before, After

Create Between, Before and After extension methods and use them to parse text.

Between, before, after. With extension methods, we easily locate Substrings. We search for substrings between two strings, before a string or after a string.

In these extension methods, we return relative substrings. This simplifies certain programs. We implement some logic with IndexOf and LastIndexOf.Substring IndexOf LastIndexOf

An example. We see the SubstringExtensions static class. This contains the extension methods Between, Before and After. We call these methods in Main.

Between: The Between method accepts 2 strings (a and b) and locates each in the source string.

Then: After some error checking, it returns the substring between them. The Before method and After method are similar.

Main: Here an input string "test" is declared. The extensions Between, Before, and After are used on it.

And: The results are printed to the console (with Console.WriteLine) after the parts are extracted.

Console

SubstringExtensions.cs implementation: C# static class SubstringExtensions { /// <summary> /// Get string value between [first] a and [last] b. /// </summary> public static string Between(this string value, string a, string b) { int posA = value.IndexOf(a); int posB = value.LastIndexOf(b); if (posA == -1) { return ""; } if (posB == -1) { return ""; } int adjustedPosA = posA + a.Length; if (adjustedPosA >= posB) { return ""; } return value.Substring(adjustedPosA, posB - adjustedPosA); } /// <summary> /// Get string value after [first] a. /// </summary> public static string Before(this string value, string a) { int posA = value.IndexOf(a); if (posA == -1) { return ""; } return value.Substring(0, posA); } /// <summary> /// Get string value after [last] a. /// </summary> public static string After(this string value, string a) { int posA = value.LastIndexOf(a); if (posA == -1) { return ""; } int adjustedPosA = posA + a.Length; if (adjustedPosA >= value.Length) { return ""; } return value.Substring(adjustedPosA); } } Main method: C# using System; class Program { static void Main() { // Input. const string test = "DEFINE:A=TWO"; // Test Between. Console.WriteLine(test.Between("DEFINE:", "=")); Console.WriteLine(test.Between(":", "=")); // Test Before. Console.WriteLine(test.Before(":")); Console.WriteLine(test.Before("=")); // Test After. Console.WriteLine(test.After(":")); Console.WriteLine(test.After("DEFINE:")); Console.WriteLine(test.After("=")); } } Output A A DEFINE DEFINE:A A=TWO A=TWO TWO

Use. Sometimes, a programmer decides a problem is best solved with a small language. However, often the requirements are not complex enough to warrant a full grammar and a parser engine.

So: You could use a simple loop along with these extensions to parse a small language.

Correctness. These methods are in use in a program I developed. There may be some errors in the error-handling logic in some cases—this has not been studied.

A summary. We provided the implementations for Between, Before, and After extensions on the string type. These implementations are not fully compatible with all requirements.

They only search for the first or last instance of the parameters. They are useful in simplifying parsing engines for simple custom languages.

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.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

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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

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C# String Between, Before, After

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