It seemed technically feasible because Python has a remarkable tool to interact with native code: the ctypes module.
The only issue is that ctypes only supports C interfaces not C++ classes so in this case it can’t directly use the YahooAPIWrapper class.
In fact it’s a minor issue because this kind of situation is well known and a well documented pattern exists to circumvent it: building a C wrapper around the C++ API.
This looks a little crazy because you now have 2 layers between the Python client code and the C# Yahoo API:
Python -> C wrapper -> C++/CLI wrapper -> C# API
So, while I don’t think this layering could have any usefulness in real-life, this was a challenging and interesting question.
Looks simple no? Well, as you know when you start to pile up heterogeneous layersunexpected issues can appear and this is exactly what happened there, and it has revealed one that is worth talking about.
So keep reading!
Sometimes we need to modify some global state, but when we do that it’s critical to ensure we leave things as we’ve found them; you know like when you lift the toilet seat: forgetting to put it down afterwards could get you in trouble!
It’s similar in programming and you need to use the right tools and practices.
In this article I’ll show you how they can be used to scope global state changes in a fluent manner, a pattern I’ve used for years to enhance reusability and readability of this kind of code.
In the first part I’ll illustrate this pattern with a small and hopefully fun example, and then in the second part I’ll describe how it can be applied to other situations like culture settings and Excel development. Continue reading →
This article replaces the previous one with the same title.
Indeed the previous C++/CLI wrapper implementation had a flaw that created memory corruption. This issue has been fixed in the following implementation.
Moreover I’ve used it as an opportunity to greatly enhance the content, especially the description of the C++/CLI wrapper implementation, design rationales being now included.
The article has been updated on the 19th of June 2016 to integrate 3 fixes:
the YahooAPIWrapper‘s destructor is correctly declared in the header file to avoid memory leaks,
the YahooAPIWrapper‘s definition/cpp file does not redefine the class and the __declspec(dllexport) metadata has been moved to the header file to avoid compilation errors,
the YahooAPIWrapper‘s and native C++ program’s implementations have been updated to take into account the new fields names of Yahoo API to avoid runtime exceptions.
When it comes to software development in a professional environment, heterogeneity is the rule not the exception: you often need to interact with systems developed with other technologies.
I’ve been recently faced with such a situation: a team that uses only native C++ needed to retrieve data using the object-oriented API of another team that develops only in .Net with C#.
This is a relatively uncommon scenario (just look at the number of articles on the subject), the standard case being new systems based on the .Net platform, developed in C# or VB.Net, needing to interact with legacy systems developed in native C++.
I’ve used the C++/CLI platform due to its unique ability to mix managed (.Net) and native code in one place and is then the ideal tool for building bridges between these two worlds using simple wrappers: the native face of the wrapper can be consumed by the legacy components and its managed face can directly use the C# API.
In this article I’ll illustrate how I’ve tackled the issue by building a simple C++/CLI wrapper, using a similar use-case: market-data retrieval from Yahoo.
If you have an important VBA code base you know how difficult it is to maintain it, not because VBA is inherently a bad or poor platform but because the developers are often either end-users not aware of good development practices or professional developers not skilled enough in VBA development who have learnt it on the job. In both cases, more often than not, you end up with poor quality source code.
There is other forces that make VBA development less appealing, as the pressure of software vendors like Microsoft who’d like to sell you not just Office but Office+Visual Studio and then promotes other technologies like .Net with languages such as C# and VB.Net. Just have a look at the evolution of the VBA editor design and capabilities since 10 years and you’ll understand that it does not benefit from fanatic development and promotion efforts.
It’s why you should avoid the headlong rush and restrict your VBA development efforts to the bare minimum: for new developments you should consider other languages and platforms like C# and VB.Net with the .Net framework as they seamlessly integrate with the Office suite, with little overhead compared to the direct integration of VBA, and give you access to a wealth of modern technologies.
But don’t be fooled by the FUD about the dangers of keeping a legacy VBA code base and do your due diligence: does the guy who suggest you a full migration will do it for free or is he paid for the job? 😉 A full migration may be a necessity: not because the platform is VBA but because the application is buggy, undocumented, out of control and using it creates a true operational risk, and this is true for any application and technology including the newest.
Then, if you have a VBA application that is working perfectly, is documented and controlled, an alternative to both the headlong rush and the full migration is the integration of .Net components with VBA, you then use a future-proof technology to develop new features and/or replace legacy features as you go along, avoiding the big-bang effect.
So now you know what to do and right now I’ll show you how to do this seamless transition from VBA to greener pastures by implementing a simple API with three popular .Net languages: C# (the king), VB.Net (the prince) and C++/CLI (the Jack of all trades, master of none).
So you have to or want to develop a native component (typically a DLL written in C or C++) with a simple API and you need to use it from another component developed in C#.
You know that you can use the DllImport mechanism and you’ve seen the 156387 tutorials that show how to make it with kernel32.dll (and by the way this is sometimes only what you need).
You’ve also seen some tutorials that to illustrate what you think is a simple matter are using huge codes and made you scream “pleeaaase get to the point!”, or the ones that ask you to setup a Visual Studio project but you want to avoid useless plumbing and understand what happens under the hood.
You’ve tried by yourself and feel you’re almost there but you still have errors and start to feel frustrated.
The good news are : first you’re right when you think DllImport is straightforward for simple interfaces, second this is the no-overengineering, no-overhead, no-nonsense, KISS tutorial for it.
So keep reading and in 10 minutes you’ll DllImport (almost) like a pro. Continue reading →
So you have deployed your awesome Excel addin in production and all is working fine for some weeks : you are enjoying your success…
But one day the phone rings and the guy at the other side is not really happy; no, he is completely upset and you could almost smell his breath when he screams.
But why? Because your awesome addin has stopped working on his workstation without notice.
Sometimes the root-cause is obvious: you have delivered a new version, but in many cases you will hardly ever know the root-cause of this annoying situation: Windows update, Office update, quick and dirty moving/installation of the addin from a workstation to another one, bad alignment of Uranus and Jupiter…
A wealth of errors can happen, then it’s hard to have them all in mind, especially when you are in a hurry and with stress you start to get mixed up. So to be as efficient as possible you’d better have a checklist and this is precisely what this article will be, enumerating all the errors I have encountered describing usual causes and solutions.
In this article I’ll show you how to create a UDF library for Excel in C# from scratch.
By “from scratch” I mean without using Visual Studio, only low-level tools : a simple text-editor like Notepad and the C# compiler.
This is of course not the way you’ll do it usually but it will hopefully help you to better understand how things work under the hood.
The pretext for this sample is a set of functions that provides financial data like the last bid and ask prices for a stock.
It uses the Yahoo finance REST API which is rich and simple and that you could use as a base for developing more advanced tools. Continue reading →