C# parse a string into an expression

Question

At me in a window the expression "a + b * 2" can be entered. How can I parse such a string into a function in the code?

Did you try anything before asking? Did you ask Google? And how do plan to use it? Do you have inputs for a, b? — Pic Mickael, May 28 '18 at 19:30
`String.Split` , `for` loop, Reflection, and some good old fashioned research/googling. Are you up to the challenge? — TheGeneral, May 28 '18 at 19:42
Also you should really take a look at https://stackoverflow.com/help/how-to-ask — TheGeneral, May 28 '18 at 19:44
what you're probably looking for is an "expression parsing library"; many exist, or you can implement it using string functions - for example, I'd probably use a modified shunting-yard algorithm to parse that — Marc Gravell, May 28 '18 at 19:46

score 0 · Answer 1 · answered May 28 '18 at 19:50

Try something like this:

class Program
{
    static void Main(string[] args)
    {
        var a = 1;
        var b = 2;
        Console.WriteLine(FN_ParseSnippet($"{a} + {b} * 2"));
        Console.ReadKey();
    }

    public static object FN_ParseSnippet(string snippet)
    {
        object ret = null;

        var usingList = new List<string>();
        usingList.Add("System");
        usingList.Add("System.Collections.Generic");
        usingList.Add("System.Text");
        usingList.Add("Microsoft.CSharp");


        //Create method
        CodeMemberMethod pMethod = new CodeMemberMethod();
        pMethod.Name = "Execute";
        pMethod.Attributes = MemberAttributes.Public;
        pMethod.ReturnType = new CodeTypeReference(typeof(object));
        pMethod.Statements.Add(new CodeSnippetExpression(" return " + snippet));

        //Create Class
        CodeTypeDeclaration pClass = new System.CodeDom.CodeTypeDeclaration("Compilator");
        pClass.Attributes = MemberAttributes.Public;
        pClass.Members.Add(pMethod);
        //Create Namespace
        CodeNamespace pNamespace = new CodeNamespace("MyNamespace");
        pNamespace.Types.Add(pClass);
        foreach (string sUsing in usingList)
            pNamespace.Imports.Add(new CodeNamespaceImport(sUsing));

        //Create compile unit
        CodeCompileUnit pUnit = new CodeCompileUnit();
        pUnit.Namespaces.Add(pNamespace);


        CompilerParameters param = new CompilerParameters();
        param.GenerateInMemory = true;
        List<AssemblyName> pReferencedAssemblys = new List<AssemblyName>();
        pReferencedAssemblys = Assembly.GetExecutingAssembly().GetReferencedAssemblies().ToList();
        pReferencedAssemblys.Add(Assembly.GetExecutingAssembly().GetName());
        pReferencedAssemblys.Add(Assembly.GetCallingAssembly().GetName());
        foreach (AssemblyName asmName in pReferencedAssemblys)
        {
            Assembly asm = Assembly.Load(asmName);
            param.ReferencedAssemblies.Add(asm.Location);
        }

        //Compile
        CompilerResults pResults = (new CSharpCodeProvider()).CreateCompiler().CompileAssemblyFromDom(param, pUnit);

        if (pResults.Errors != null && pResults.Errors.Count > 0)
        {
            //foreach (CompilerError pError in pResults.Errors)
            //    MessageBox.Show(pError.ToString());

        }

        var instance = pResults.CompiledAssembly.CreateInstance("MyNamespace.Compilator");
        ret = instance.GetType().InvokeMember("Execute", BindingFlags.InvokeMethod, null, instance, null);

        return ret;
    }

}

C# parse a string into an expression

1 Answers1