Never Nester, Goto, RAII, and Defer

Coding when you are using an OS or library that requires a series of calls that build on each other to get the final result requires a set of checks to make sure each stage is successful. If some of the stages also require it partner call to free/close/destroy the items, then the programming logic requires you to be careful in how you tear down the items if there is an error in the middle of the process.

This can be coded several ways, and this post discusses a series of approaches in C++. The code selected for the example is performing Windows OS calls. These are done at the lowest API level without any other library or framework. The code has three places where tear down is required. The flow is complex enough to stop a simple reorganisation of the code to perform the same task. There is no addition error management present so make it easier to read. It is a fully working program and it gets a list of USB devices that the program is allowed access to.


Reasons for Using C++ 17

Using the logic that we should use tools that are as simple as possible and only adopt complexity where it is absolutely necessary, it feels like I could use a very early version of C++. What follows are the reasons why I have increased that to C++17. The idea will be to only use these feature and no more. Any new use will be add to this page.

#if !((defined(_MSVC_LANG) && _MSVC_LANG >= 201703L) || __cplusplus >= 201703L)
    #error Requires C++17 or higher

Screen Find – Seeing the Wood in the Trees

I hope you have a nice big screen – or several of them. Nice huh?

Well all this real estate comes with a price. Some times the screens can hold so much information it is hard to find what you are looking for. Would it not be nice to be able to search for the word you are looking for in a huge list of dense text?

Sure almost every app has search, but can you search the dialogue boxes, the drop down menus, the image of a poster?

So why not have a system wide special key combo that triggered a find dialogue box. Type in ‘comment’ and the screens are captured, OCR’ed and then if the text is found an overlay highlight shows you where the word is.


C++ Coding Standards

The following is not intended to generate a holy war, but merely a place for me to remind myself of the decisions I took along the way to get to a consistent style for any new code that I write.

#pragma warning( push, 3 )
#include <stdio.h>
#pragma warning( pop )

// /Wall Used. Compiler warnings turned off.
#pragma warning (disable :  5045) // Spectre code insertion warning.

class entity
    static constexpr size_t     _maxEntities = 1000;
    entity(char* name)
        _name = name;
    void set()
    char    _name[8];

inline float _floor(const float& a)
    if (a == 0.0f) return 0.0f;
    return floorf(a);

C Strings in C++ and Deep Copies

I was told on Stack Overflow:

“A pointer is just a pointer.”

And that is true of course. To go beyond that we have structures and classes which have explicit construction and operators. However, C++ has inherited C strings which are just a pointer to the first char, but they also have a long history where the construction and operations are well known. So, when a C String is given to a map or vector, it may be thought that it could be doing a deep copy. After all, it is known (by implicit rules) how this could be completed. The size is defined. It is just not stored. Also, the storage is clear – just not managed.


Easy to Make Mistakes in Class Inheritance

This started out as a task to learn simple class inheritance. To work out the syntax and idiomatic way to use them in C++. I just kept typing things that I thought would work and the compiler would slowly teach me what was wrong.

class rectangle : public shape
    rectangle(float half) : shape(half)

Learning C++

This is a series of things that I found out when learning C++. The approach is going to be non-standard and likely to annoy any normal C++ professional. I am interested in languages in general and so I will be doing all my early code without STL at all. I want to learn what features the language offers before starting to use the standard libraries. To this end I try to do do simple version of the features that are already available. That way I can see how these features are implemented in the standard libraries. To me, that feels like a important advantage in learning a language. I did try to read the code for the libraries but it has a lot of very nuanced additions that I will only get to understand much later on. The code is still interesting to step through however as it does offer clues as to how to unpick various implementations.


Asking Stack Overflow the best way to do Template Specialisation

In learning C++ I dug in and tried to use classes and templates to solve what feels like a typical use case. I found that what I needed was Template Specialisation and that C++ does not support this very well. I came up with 3 different methods and wanted to check what others though was we the best approach. If there was a “preferred idiom in C++”, or an even better solution.