Author Archives: Glennan Carnie

About Glennan Carnie

Glennan is an embedded systems and software engineer with over 20 years experience, mostly in high-integrity systems for the defence and aerospace industry. He specialises in C++, UML, software modelling, Systems Engineering and process development.

Bitesize Modern C++ : noexcept

We have some basic problems when trying to define error management in C:

There is no “standard” way of reporting errors. Each company / project / programmer has a different approach
Given the basic approaches, you cannot guarantee the error will be acted upon.
There are difficulties with error propagation; particularly with nested calls.

The C++ exception mechanism gives us a facility to deal with run-time errors or fault conditions that make further execution of a program meaningless.

In C++98 it is possible to specify […]

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Bitesize Modern C++ : Override and Final

Override specifier

In C++98 using polymorphic types can sometimes lead to head-scratching results:

On the face of it this code looks sound; indeed it will compile with no errors or warnings. However, when it runs the Base version of op() will be executed!

The reason? Derived’s version of op() is not actually an override of Base::op since int and long are considered different types (it’s actually a conversion between an int and a long, not a promotion)

The compiler is more than happy to […]

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Bitesize Modern C++ : Range-for loops

If you’re using container classes in your C++ code (and you probably should be, even if it’s just std::array) then one of the things you’re going to want to do (a lot) is iterate through the container accessing each member in turn.

Without resorting to STL algorithms we could use a for-loop to iterate through the container.

If the above is baffling to you there are plenty of useful little tutorials on the STL on the Internet (For example, this one)

We could […]

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Bitesize Modern C++: std::initializer_list

An aggregate type in C++ is a type that can be initialised with a brace-enclosed list of initialisers. C++ contains three basic aggregate types, inherited from C:

arrays
structures
unions

Since one of the design goals of C++ was to emulate the behaviour of built-in types it seems reasonable that you should be able to initialise user-defined aggregate types (containers, etc.) in the same way.

A std::initializer_list is a template class that allows a user-defined type to become an aggregate type.

When initialiser […]

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Bitesize Modern C++: Uniform initialization

C++98 has a frustratingly large number of ways of initialising an object.

(Note: not all these initialisations may be valid at the same time, or at all. We’re interested in the syntax here, not the semantics of the class X)

One of the design goals in C++11 was uniform initialisation syntax. That is, wherever possible, to use a consistent syntax for initialising any object. The aim was to make the language more consistent, therefore easier to learn (for beginners), and leading to […]

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Bitesize Modern C++: using aliases

In a C++ program it is common to create type aliases using typedef. A type alias is not a new type, simply a new name for an existing declaration. Used carefully, typedef can improve the readability and maintainability of code – particularly when dealing with complex declarations.

In C++11 typedef can be replaced with a using-alias. This performs the same function as a typedef; although the syntax is (arguably) more readable. A using-alias can be used wherever a typedef could be […]

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Bitesize Modern C++: nullptr

What’s the value of a null pointer?

0
NULL
NUL

No doubt you’ve been involved in the (always heated) discussions about which is the correct one (By the way, if you said NUL you need to take yourself to one side and give yourself a stern talking to).

The arguments tend to go something like this:

0 is the only ‘well-known’ value a pointer can be set to that can be checked.
NULL is more explicit than just writing zero (even though it is just a […]

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Bitesize Modern C++: enum class

Enumerated types in C++ give a trivial simulation of symbolic types – that is, objects whose instances have unique, human-readable values. In C++ enumerations are essentially named integers that are either assigned values implicitly by the compiler or explicitly by the programmer (or a combination of both)

C++ enum types inherit their semantics from C with some additions:

enum objects are now first-class types
enums may be implicitly converted to integers; but the reverse is not true

Another characteristic illustrated in the […]

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Bitesize Modern C++ : static_assert

C’s assert library is a useful tool for catching invalid invariants (conditions that must hold true in order for your system to operate as specified) in your program. The big problem with assert is that it’s a run-time check; in many cases the best you can do  to recover from an assert failure is restart the system or put it into a quiescent state.

In a lot of cases the (faulty) invariants could be detected at compile-time but in C++98 there […]

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Bitesize Modern C++ : constexpr

A constant expression is an expression that can be evaluated at compile-time. The const qualifier gives a weak guarantee of a constant expression – a const-qualified type may not be changed after initialisation but that does not guarantee it will be initialised at compile-time. For example:

C++11 introduces a strong form of constant expression, constexpr, which also expands the capabilities of compile-time evaluation.

constexpr objects

A constexpr variable is essentially the same as qualifying the type as const with the additional requirement that […]

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