计算数学表达式的最佳和最短方法

eval

using Microsoft.JScript;        // needs a reference to Microsoft.JScript.dll
using Microsoft.JScript.Vsa;    // needs a reference to Microsoft.Vsa.dll

// ...

string expr = "7 + (5 * 4)";
Console.WriteLine(JScriptEval(expr));    // displays 27

// ...

public static double JScriptEval(string expr)
{
    // error checking etc removed for brevity
    return double.Parse(Eval.JScriptEvaluate(expr, _engine).ToString());
}

private static readonly VsaEngine _engine = VsaEngine.CreateEngine();

CodeSnippetCompileUnit

• 系统。CodeDom;

string source = @"
class MyType
{
    public static int Evaluate(<!parameters!>)
    {
        return <!expression!>;
    }
}
";

string parameters = "int a, int b, int c";
string expression = "a + b * c";

string finalSource = source.Replace("<!parameters!>", parameters).Replace("<!expression!>", expression);

CodeSnippetCompileUnit compileUnit = new CodeSnippetCompileUnit(finalSource);
CodeDomProvider provider = new CSharpCodeProvider();

CompilerParameters parameters = new CompilerParameters();

CompilerResults results = provider.CompileAssemblyFromDom(parameters, compileUnit);

Type type = results.CompiledAssembly.GetType("MyType");
MethodInfo method = type.GetMethod("Evaluate");

// The first parameter is the instance to invoke the method on. Because our Evaluate method is static, we pass null.
int result = (int)method.Invoke(null, new object[] { 4, -3, 2 });

ncalc codeplex

.

Eval

class JsMath
{
    static function Eval(expression : String) : double
    {
        return eval(expression);
    };
}

将其编译成类库:

jsc /t:library JsMath.js

double result = JsMath.Eval(expression);

check it out here

(我们用它来设置“人类可读”的业务规则,数据由SQL server数据库提供)

示例可用,开发人员提供了非常好的支持(查看网站论坛)。

我认为这是最好的办法。 Petar Repac's answer 使用DataColumn对象的'expression'参数可以非常轻松地解决这个问题:

static double Evaluate(string expression)
{
    var loDataTable = new DataTable();
    var loDataColumn = new DataColumn("Eval", typeof(double), expression);
    loDataTable.Columns.Add(loDataColumn);
    loDataTable.Rows.Add(0);
    return (double)(loDataTable.Rows[0]["Eval"]);
}

Math-Expression-Evaluator 2.5+5.9 , 17.89-2.47+7.16 , 5/2/2+1.5*3+4.58 (((9-6/2)*2-4)/2-6-1)/(2+24/(2+4))

var a = 6;
var b = 4.32m;
var c = 24.15m;
var engine = new ExpressionEvaluator();
engine.Evaluate("(((9-a/2)*2-b)/2-a-1)/(2+c/(2+4))", new { a, b, c});

dynamic dynamicEngine = new ExpressionEvaluator();

var a = 6;
var b = 4.5m;
var c = 2.6m;

dynamicEngine.Evaluate("(c+b)*a", a: 6, b: 4.5, c: 2.6);

    string finalSource = ...;
    IEnumerable<Assembly> references = ...;

    var compilation = CSharpCompilation.Create("Dynamic",
        new[] { 
            SyntaxFactory.ParseSyntaxTree(
                finalSource,
                CSharpParseOptions.Default
                    .WithLanguageVersion(LanguageVersion.Latest)
            ) },
        references.Select(a => MetadataReference.CreateFromFile(a.Location)),

        new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)
            .WithAssemblyIdentityComparer(DesktopAssemblyIdentityComparer.Default)
    );

    using var ms = new MemoryStream();
    var e = compilation.Emit(ms);
    if (!e.Success)
        throw new Exception("Compilation failed");
    ms.Seek(0, SeekOrigin.Begin);

    var context = new AssemblyLoadContext(null, true);
    var assembly = context.LoadFromStream(ms);

    AppDomain.CurrentDomain.GetAssemblies().Where(a => a.GetName().Name == "netstandard").Single(),
    typeof(object).Assembly