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best_practices [2016/03/11 12:45] – [Tips & tricks] jmgrbest_practices [2023/04/25 16:52] (current) – external edit 127.0.0.1
Line 5: Line 5:
 ==== Tips & tricks ==== ==== Tips & tricks ====
  
-=== Always initialise primitive variables (other types do not require this) ===+=== Always initialize primitive variables (other types do not require this) ===
  
 <code cpp> <code cpp>
Line 14: Line 14:
 // Good // Good
 int myVariable{}; int myVariable{};
-std::string myString;+std::string myString; // std::string is not a primitive variable, so initialization is optional
 </code> </code>
  
Line 108: Line 108:
 MyObject *object = new MyObject(parentObject); MyObject *object = new MyObject(parentObject);
 </code> </code>
 +
 +Note the use of std::make_unique here; it should be used instead of //new// when using std::unique_ptr.
  
 === Never mix C and C++ code === === Never mix C and C++ code ===
Line 181: Line 183:
 </code> </code>
  
-=== When using events, prefer using lambdas (nameless functions) instead of static functions ===+=== When using events, prefer using lambdas (anonymous functions) instead of static functions ===
  
 <code cpp> <code cpp>
Line 332: Line 334:
 Color otherColor = static_cast<Color>(colorAsInteger); Color otherColor = static_cast<Color>(colorAsInteger);
 </code> </code>
 +
 +When dealing with QObject-based classes you should use [[http://doc.qt.io/qt-5/qobject.html#qobject_cast|qobject_cast]].
 +
 +=== Header files should not depend on other #includes ===
 +To test this, just include your header in an empty source file, if it doesn't compile then you should add the missing #include directives.
 +
 +=== Header files should be grouped by library and sorted, system headers should be at the bottom ===
 +This helps readability. Putting system headers at the bottom helps ensuring that the previous rule is enforced.
 +
 +<code cpp>
 +// Local headers
 +#include "MyClass.hpp"
 +
 +// Library headers
 +#include <QDebug>
 +
 +// System headers
 +#include <cmath>
 +#include <cstdio>
 +</code>
 +
 +=== Prevent dependency contamination ===
 +Use case: you are using an "enum" or "#defines" from a system header, lets say Windows.h.
 +
 +<file cpp myclass.hpp>
 +#pragma once
 +
 +#include <Windows.h>
 +
 +class MyClass final
 +{
 +public:
 +    MyClass() = default;
 +    
 +private:
 +    HWND m_window;
 +};
 +</file>
 +
 +In this case, every file #including "myclass.hpp" will also implicitly #include Windows.h. Ouch.
 +This dependency cannot be removed because you need to #include Windows.h to be able to use the type HWND.
 +
 +Solution: here we can use the "private implementation" idiom, or "pimpl". I consists in having all the member variables in a separate struct.
 +
 +<file cpp myclass_private.hpp>
 +#pragma once
 +
 +#include <Windows.h>
 +
 +struct MyClass_Private
 +{
 +    HWND window;
 +};
 +</file>
 +
 +<file cpp myclass.hpp>
 +#pragma once
 +
 +#include <memory>
 +
 +struct MyClass_Private;
 +
 +class MyClass final
 +{
 +public:
 +    MyClass();
 +    
 +private:
 +    std::unique_ptr<MyClass_Private> m_private;
 +};
 +</file>
 +
 +<file cpp myclass.cpp>
 +#include "myclass_private.hpp"
 +#include "myclass.hpp"
 +
 +MyClass::MyClass():
 +    m_private{std::make_unique<MyClass_Private>()}
 +{
 +    // Access window by using m_private->window
 +}
 +</file>
 +
 +And that's it. It is indeed an increase in complexity and has a slight impact on performance, but reduces compilation time and prevents clashes between symbols and #defines (and Windows.h creates a huge pile of mess when included).
  
 === Write small functions instead of huge ones === === Write small functions instead of huge ones ===
 === Never call virtual functions from a constructor === === Never call virtual functions from a constructor ===
 Reference: [[https://stackoverflow.com/questions/496440/c-virtual-function-from-constructor]] Reference: [[https://stackoverflow.com/questions/496440/c-virtual-function-from-constructor]]
 +=== Classes and variables ===
 +You should not consider a class as a collection of variables, but rather like a service provider. That is the reason why you should put the public functions first, before the private ones. Variables should be put at the end, since they are an implementation detail.
 +
 +===== Comments =====
 +What amount of comments should you write? Too many comments will make the code unreadable (see AutoHotKey for an example).
 +
 +TODO: Add something about Doxygen and how to write compatible comments
 +
 +<code cpp>
 +// Bad
 +void stuff(int blih)
 +{
 +    int blah = 5; // We set blah to 5 here
 +    int bloh = std::max(blih, 8); // Here we compute the maximum value between blih and 8, and then we store the result in a variable called bloh
 +    
 +    //...  
 +    
 +    return blah; // We return the value of the variable blah of type integer. We then terminate this function and continue our merry way into our program. Yep. That's it. Bye.
 +}
 +
 +// Good
 +// Note that this "example" has other issues: the function and the variables have meaningless names, and there is a magic value
 +void stuff(int blih)
 +{
 +    int blah = 5;
 +    // We need to compute bloh here because...
 +    int bloh = std::max(blih, 8);
 +    
 +    //...  
 +    
 +    return blah;
 +}
 +</code>
 +
 ===== Qt specific ===== ===== Qt specific =====
  
best_practices.1457700355.txt.gz · Last modified: 2023/04/25 16:52 (external edit)