With python, I can use if __name__ == "__main__": for using the module both as a library and a program.
Can I mimic this feature in C#?
I see a class in C# can have a 'static void Main()', but I'm not sure if every class can have a Main() without a problem.
ADDED
/m:CLASS_NAME is a way to specify the class to run the Main().
You can put a Main method in as many classes as you like, although only one can be an entry point for an application. (For talks, I often have a main method in every class, and use a helper library to present all of those pseudo-entry-points when I run the project.)
Likewise you can definitely add a reference to a .exe assembly and treat it like a library. For example, you could make a unit testing assembly work like a class library in most cases, but also write a main method so that you could just run it to execute the tests without a GUI or whatever.
You can compile a C# project as a program (executable) with a Main() method, and you'd still be able to use it as a library. No special syntax required.
You could add a Main() method to every class, but I doubt it's useful.
.NET applications usually have different structures than Python ones; trying to fit the same programming model is unlikely to get you good results.
C# project files specify a startup object when multiple entry points are available.
See this article for more info.
Related
I was wondering how I could program like a certain API, I have written an algorithm that I want to publish so people can use it, but I don't want people to see the code, and steal it? Paranoid, I know, but still.
How is that made, so for instance I can in a C# script (the API would also be written in C#), include it (with using ApiName) and use the functions inside, for instance if the API has a function that I program like "void Calculate(float x, float y)", and then from a script they can call "Calculate(100, 200)" for instance. I know it's somehow possible because of the Windows API, etc. Also is creating a Class Library the same thing?
Before any code runs, it is either compiled or interpreted into binary. This is highly simplified but that is the general idea. As long as a library or API provides an interface like names of functions, the implementation itself can be compiled and still work.
For C#, NuGet is a good example, you can create a NuGet of your code (see https://learn.microsoft.com/en-us/nuget/create-packages/creating-a-package) where the public function and method signatures will be visible and usable but the implementations will be compiled. DLLs work in a similar way. You can reference them and call their public members but not see the code unless you use a tool to decompile them.
I am designing an application that will need to create some C# classes at runtime. I would like to be able to convert those classes into javascript equivalents. For example I might have a C# class that looks like
public class Person
{
public int Score { get; set; }
public bool IsScoreValid()
{//code in real implementation would be more complex and make use of various properties
return Score > 0 && Score <= 100;
}
}
The trick here is that the Person class here will be created at runtime based on some configuration. I do not have control over the code in the IsScoreValid method and it could change while the application is running. I only know that it is valid C# code. I need a robust way to convert this class into a javascript equivalent, and I need to be able to perform this conversion at runtime. Would Bridge.net be a good way to convert this javascript? Can Bridge.net compiler be invoked at runtime?
If it is possible? It indeed is, see http://deck.net/. But unfortunately the project is not open source. Basically it is a project that directly calls Bridge.Translator.Translate() method with the right parameters to build the file.
A web project implementing real time bridge compilation would need to be capable of handling server-side calls, like webservices (ashx) in Asp.NET, but you can also do that via cgi-bin or php from linux/osx, using the Bridge CLI if you make commandline calls, or wire up a wrapper to call Bridge.Translator directly. That would need to be a Mono-capable binary to be linked against Bridge.Translator on Linux/osx though.
While the deck.net project is not open, Bridge itself is, so you have full access to see how to call Bridge's Translate() method from either the Bridge.Builder or Bridge CLI open projects.
Bridge Builder console app sources at Bridge main repository
Bridge Translator sources at Bridge main repository
Bridge CLI sources
But if you want the code not to care about references, like missing the definition or a prototype for IsScoreValid(), then that would be a problem to work with Bridge. It would require at least the method to be prototyped and marked External before it could accept the call; as the code tree is built thru roslyn, the c# code must be complete and buildable. (or else, could we call it proper C#? maybe, in your case, you don't really require full-fledged C#)
I've recently had to migrate to the C# world. Coming from the Java land, I could add a public static void main(String[] args) method to any class and select to run that class from Eclipse/Netbeans for any code/logic that I wanted to quickly test.
Is there an equivalent of the same capability in C#.Net/Visual Studio? I've tried doing that and the best I can do is to execute it from the command prompt via csc.exe. However, for some reason, it complains about not finding the relevant DLLs - it seems to expect to run that class in complete isolation without any dependency on "external code" (i.e., code residing in that VS project/solution where the class resides).
Reason for this capability: All project files are marked as class libraries and sometimes I just wish to check if a particular set of methods/data/logic will work as expected with the current code base. In Java, I'd quickly write it in the main method and execute that class to see how it goes prior to committing it to version control. However, there seems to be no easy way to trigger the execution of "my class" with all dependencies correctly handled by csc.exe
Current Solution: Add this testing code to the unit test project and select to execute that particular "test" so as to check if the idea seems to work fine (it may fire DB calls or webservice class etc., and not be purely a logical flow of computation). This seems to work fine and is my current way of doing things. I was wondering if the Main method was even possible/recommended.
Question: Is this even possible with C#/VS or not recommended?
Update: I can't add a console project just to achieve this since the addition of projects is tightly controlled by the source control team. Hence the question of the Main method 'hack' for quick and dirty checks/tests.
Your project type needs to be Console Application for it to "recognize" a Program.Main method, not Class Library. The intent is for a Class Library to be an encapsulated grouping of functionality that can only be accessed by a project that is set up to allow for user input. Those can be a Console Application, Web project (MVC/API), or Desktop (WPF).
If you just want to execute a test against the code within a Class Library project, you can also create a Unit Test project, add a reference and execute very explicit tests against the functionality you're looking to achieve.
You can find out the differences between the different project types by examining the .csproj files in your favorite text editor.
In Visual Studio go New->Project then select Console Application (in Windows\Classic Desktop in VS2015). This gives you a basic console application with...
static void Main(string[] args)
{
}
setup and ready to go. However for simply trying out code you may find this cumbersome (creating a new project and folder just to test code) and for testing code (that doesn't rely on existing libraries) you could use something like .NET Fiddle...
https://dotnetfiddle.net/
Where you can quickly create and test code there and run it via the browser.
I'm a bit new at this so bear with me. I'm currently learning C# and Java and one of their similarities is that the main function needs to be encapsulated within a class. For example
public class HelloWorld {
public static void main(String[] args) {
// Some Code
}
}
Now I understand that main is often the "entry point" when you run the program. So basically, your program will start executing wherever the main function is. But I believe in both languages you can have multiple main functions within multiple classes. So when I compile a project with multiple main functions, where is the "entry point"? How does the compiler know where to start?
In Java, the computer determines the "entry point" when you actually execute the program, not when you compile. For example, from the command-line
java MyClass
searches for main() in MyClass. All other main() functions are ignored.
If you are using an IDE, then you can set which class contains the main() function that you want to use.
In .NET, you can define which class contains the Main method you want to use when you're compiling.
http://msdn.microsoft.com/en-us/library/x3eht538.aspx
In Java, if you're bundling to a jar, you can define your entry point in the jar's manifest.
http://docs.oracle.com/javase/tutorial/deployment/jar/appman.html
In C#, you can use multiple Main methods.
If there are multiple Main methods, the compiler doesn't know which entry point to use and hence it will show you an error.
You need to specify the Main method to be used at compilation:
You can specify which method to be used as a compiler option in the Visual Studio development environment or through the csc compiler.
The main class is a special class for only one reason: when you run the Java Virtual Machine, that function is what the JVM calls. It is essentially like any other function, and in fact you can call one class's main function from another class.
When you compile a project with multiple classes, you tell the JVM to run the class with the main class you want to use, like so:
java SomeClass
and it will run the main method of SomeClass, assuming that SomeClass is compiled and that the appropriate compiled file is in your classpath. (That is something you'll have to work out with your particular OS, but I think it's fairly usual for the -cp option to specify a classpath). So this:
java -cp /home/MyName Someclass
will run the main function of SomeClass in the directory /home/MyName
In C#, you specify the entry point using the /main: compiler option.
Consider the following code containing two main() functions:
namespace Application {
class ClassOne {
static void main () {
// Code here
}
}
class ClassTwo {
static void main () {
// Code here
}
}
}
To use ClassOne.main() as your entry point, you would specify the following when compiling:
csc /main:Application.ClassOne hello.cs
For multiple main functions entry point can be declared by :
To set this compiler option in the Visual Studio development environment
Open the project's Properties page.
Click the Application property page.
Modify the Startup object property.
reference : http://msdn.microsoft.com/en-us/library/x3eht538.aspx
In Java, as others pointed out, you define the class containing your main function when you run the java command.
But you could also build an executable jar, which can be run with java -jar my.jar. In this case, you need a manifest file called MANIFEST.MF in the folder META-INF in the jar. In this file, you specify the class containing the main function using the statement: Main-Class: YourClass.
The main method is static, which means it belongs to the class rather than the object. So the object won't have another main method inside it at all. It won't have an additional main-method, as main is static. So it's once per class.
If you have multiple main-methods in your project, you will specify which one to launch when starting your application
In fact, in binary file, for example, PE format in windows and ELF format in Linux or any other system, The header of binary file will specify where is the start address and there can be only one.
Which one should be the entry point? It depends on the linker. Just like #SetFreeByTruth said that you can specify it with command line parameters.
Many linkers support specifying entry point with command line parameters. for example, gnu's gld can specify entry point with parameter -e.
I don't know the behavior of Java because it is loaded by Java virtual machine.
In Visual Studio, you select the project that you want to be the entry point, right click and Set as StartUp Project.
I like to create a file full of custom functions which I have made, which I may use in another project or something. Now I don't fully understand how to go about this, normally in a language like php, you'd just create the php file and then go include("cust_lib.php") or whatever the file is called.
Now I think that the process involves the library having its own namespace, then either go using custom_lib; or custom_lib:: within the script (I don't want to get into a discussion over which is the best way to go here).
Is this right? Or should I create the library and convert it to a .dll, if so how do I go about this, what sort of syntax does a dll have inside it etc.
However if its just file within one project then I don't need to go down that route do I? I can just create the namespace and use that?
This is what I'm working for at the moment, and thought it would be something like this
namespace Custom_Lib{
~~functions to go here~~
}
However the functions have to exist within a class don't they? So that becomes something like
namespace Custom_Lib{
class custom_lib{
public string function1(string input){
return input;
}
}
}
So some help, pointers, examples would be appreciated so I can wrap my head around this
Thanks,
Psy.
(Yes I call them functions, that just comes from a long php/js etc background)
The normal approach would be to create a Class Library project, put your classes and methods in that project, making sure that those you want to expose are public. Then you add a reference to the resulting dll file in the client projects and you will have the functionality from the class library available to you.
Even if you decide to put it all into one single file, I would still recommend you to make it a class library since I imagine that will make it easier to maintain. For instance, consider the following scenarios:
You decide to put it in a file and include a copy of that file in all projects where you want to use it. Later you find a bug in the code. Now you will have a number of copies of the file in which to correct the bug.
You decide to put it in a file and include that same file in all projects. Now, if you want to change some behaviour in it, you will alter the behavior for all projects using it.
In those two cases, keeping it as a separate project will facilitate things for you:
You will have only one copy of the code to maintain
You can decide whether or not to update the dll used by a certain project when you make updates to the class library.
Regarding the syntax issues: yes all methods must exist within a class. However, if the class is merely a container of the methods, you can make it (and the methods static):
public static class CustomLib
{
public static string GetSomethingInteresting(int input)
{
// your code here...
}
}
That way you will not need to create an instance of CustomLib, but can just call the method:
string meaningOfLife = CustomLib.GetSomethingInteresting(42);
In addition to Fredrik Mörk's well-written and spot-on response, I'd add this:
Avoid creating a single class that is a kitchen-sink collection of functions/methods.
Instead, group related methods into smaller classes so that it's easier for you and consumers of your library to find the functionality they want. Also, if your library makes use of class-level variables, you can limit their scope.
Further, if you decide later on to add threading capabilities to your library, or if your library is used in a multi-threaded application, static methods will likely become a nightmare for you. This is a serious concern, and shouldn't be overlooked.
There no question here. You answered it yourself. Yes, you have to construct a class to include all helper methods. And yes, you can either compile it to a dll if you want to reuse in multiple projects it or just add the source file to the project.
Usually I declare the helper class and all functions as static to avoid initiating the class each time I use it.