This post is part of a series about building a simple mathematical expression evaluator. For previous posts and full source code see Table of Contents.
Introduction In previous part we added support for variables but it has a big disadvantage: values of the variables are bound by position and not by name. This means that you should pass values for the variables in the same order as they appear in the expression. For example the following test will fail:
Introduction In part two of this series we built an expression evaluator capable of parsing expressions with parentheses. In this part we are going to add support for expression with variables.
Introduction In previous post I showed how to build a simple expression evaluator using expression trees. Although it works fine it has some drawbacks:
It does not support parentheses. It does not support variables. In some cases the result can be wrong as the parser is not using left to right parsing. It is compiling delegates for every expression which results in slower execution. To solve these issues we will use a different algorithm and deal with all points except variable support.
Introduction This is first part of a series about writing expression evaluator in C#. Even though there are several of them available already I decided to write my own as this one is based on expression trees and is very simple. The evaluator supports numeric expressions as well as expression with parameters.
This is table of contents for Building Expression Evaluator with Expression Trees in C# series. We are going to build a simple mathematical expression evaluator in C# using expression trees. The library supports simple expressions such as 2.5+5.9, 17.89-2.47+7.16, 5/2/2+1.5*3+4.58, expressions with parentheses (((9-6/2)*2-4)/2-6-1)/(2+24/(2+4)) and expressions with variables:
var a = 6; var b = 4.32m; var c = 24.15m; Assert.That(engine.Evaluate("(((9-a/2)*2-b)/2-a-1)/(2+c/(2+4))", a, b, c), Is.EqualTo((((9 - a / 2) * 2 - b) / 2 - a - 1) / (2 + c / (2 + 4)))); At the end of the series full source code will be available at github and the library will be published to NuGet.
AppDomain.AssemblyResolve event can be used to load referenced assemblies at runtime. This can be useful in multiple scenarios: you can use it to load a library from a different location or load a library based on bitness or load a library which is embedded in the executable file. In all cases there are some tips and tricks which can help you to easily implement the event handler and avoid exceptions.
As you know retrieving process path in .Net is quite straightforward. For example if you have process instance someProcess you can get the process path by accessing someProcess.MainModule.FileName However for elevated processes the previous code snippet throws Win32Exception.
While working on an application which makes use of Process class I found several bugs which occur in special conditions. More specifically accessing StartTime or HasExited properties causes a Win32Exception with NativeErrorCode equal to five. This indicates that the exception is caused by not having enough rights to retrieve the required information.
The exception occurs under the following conditions: