C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significantly over time, and modern C++ now has object-oriented, generic, and functional features in addition to facilities for low-level memory manipulation. It is almost always implemented as a compiled language, and many vendors provide C++ compilers, including the Free Software Foundation, LLVM, Microsoft, Intel, Embarcadero, Oracle, and IBM, so it is available on many platforms.[13]
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In 1982, Stroustrup started to develop a successor to C with Classes, which he named "C++" (++ being the increment operator in C) after going through several other names. New features were added, including virtual functions, function name and operator overloading, references, constants, type-safe free-store memory allocation (new/delete), improved type checking, and BCPL style single-line comments with two forward slashes (//). Furthermore, Stroustrup developed a new, standalone compiler for C++, Cfront.
C++ templates enable generic programming. C++ supports function, class, alias, and variable templates. Templates may be parameterized by types, compile-time constants, and other templates. Templates are implemented by instantiation at compile-time. To instantiate a template, compilers substitute specific arguments for a template's parameters to generate a concrete function or class instance. Some substitutions are not possible; these are eliminated by an overload resolution policy described by the phrase "Substitution failure is not an error" (SFINAE). Templates are a powerful tool that can be used for generic programming, template metaprogramming, and code optimization, but this power implies a cost. Template use may increase code size, because each template instantiation produces a copy of the template code: one for each set of template arguments, however, this is the same or smaller amount of code that would be generated if the code was written by hand.[70] This is in contrast to run-time generics seen in other languages (e.g., Java) where at compile-time the type is erased and a single template body is preserved.
Overloadable operators are also an essential part of many advanced C++ programming techniques, such as smart pointers. Overloading an operator does not change the precedence of calculations involving the operator, nor does it change the number of operands that the operator uses (any operand may however be ignored by the operator, though it will be evaluated prior to execution). Overloaded "&&" and "" operators lose their short-circuit evaluation property.
Templates in C++ provide a sophisticated mechanism for writing generic, polymorphic code (i.e. parametric polymorphism). In particular, through the curiously recurring template pattern, it's possible to implement a form of static polymorphism that closely mimics the syntax for overriding virtual functions. Because C++ templates are type-aware and Turing-complete, they can also be used to let the compiler resolve recursive conditionals and generate substantial programs through template metaprogramming. Contrary to some opinion, template code will not generate a bulk code after compilation with the proper compiler settings.[70]
It is also possible to raise exceptions purposefully, using the throw keyword; these exceptions are handled in the usual way. In some cases, exceptions cannot be used due to technical reasons. One such example is a critical component of an embedded system, where every operation must be guaranteed to complete within a specified amount of time. This cannot be determined with exceptions as no tools exist to determine the maximum time required for an exception to be handled.[83]
The C++ Core Guidelines[85] are an initiative led by Bjarne Stroustrup, the inventor of C++, and Herb Sutter, the convener and chair of the C++ ISO Working Group, to help programmers write 'Modern C++' by using best practices for the language standards C++11 and newer, and to help developers of compilers and static checking tools to create rules for catching bad programming practices.
To give compiler vendors greater freedom, the C++ standards committee decided not to dictate the implementation of name mangling, exception handling, and other implementation-specific features. The downside of this decision is that object code produced by different compilers is expected to be incompatible. There were, however, attempts to standardize compilers for particular machines or operating systems (for example C++ ABI),[89] though they seem to be largely abandoned now.
These guidelines are not meant to be complete or exact in every language-technical detail.For the final word on language definition issues, including every exception to general rules and every feature, see the ISO C++ standard.
This is not a language manual.It is meant to be helpful, rather than complete, fully accurate on technical details, or a guide to existing code.Recommended information sources can be found in the references.
Extensions often do not have rigorously defined semantics. Even extensions thatare common and implemented by multiple compilers might have slightly differentbehaviors and edge case behavior as a direct result of not having a rigorousstandard definition. With sufficient use of any such extension, expectedportability will be impacted.
constexpr does not guarantee compile-time evaluation;it just guarantees that the function can be evaluated at compile time for constant expression arguments if the programmer requires it or the compiler decides to do so to optimize.
Any API that might eventually depend on high-level run-time configuration orbusiness logic should not be made constexpr. Such customization can not beevaluated by the compiler, and any constexpr functions that depended uponthat API would have to be refactored or drop constexpr.
Sometimes, we need to pass an object to a function to manipulate its state.In such cases, passing the object by reference T& is usually the right technique.Explicitly passing an in-out parameter back out again as a return value is often not necessary.For example:
A destructor (either user-defined or compiler-generated) is implicitly declared noexcept (independently of what code is in its body) if all of the members of its class have noexcept destructors. By explicitly marking destructors noexcept, an author guards against the destructor becoming implicitly noexcept(false) through the addition or modification of a class member.
There are domains, such as some hard-real-time systems (think airplane controls) where (without additional tool support) exception handling is not sufficiently predictable from a timing perspective.There the is_valid() technique must be used. In such cases, check is_valid() consistently and immediately to simulate RAII.
Statically allocated objects of built-in types are by default initialized to 0, but local built-in variables are not.Beware that your compiler might default initialize local built-in variables, whereas an optimized build will not.Thus, code like the example above might appear to work, but it relies on undefined behavior.Assuming that you want initialization, an explicit default initialization can help:
But what if you can get significantly better performance by not making a temporary copy? Consider a simple Vector intended for a domain where assignment of large, equal-sized Vectors is common. In this case, the copy of elements implied by the swap implementation technique could cause an order of magnitude increase in cost:
Readability.Detection of mistakes.Writing explicit virtual, override, or final is self-documenting and enables the compiler to catch mismatch of types and/or names between base and derived classes. However, writing more than one of these three is both redundant and a potential source of errors.
How can we gain the benefit of stable hierarchies from implementation hierarchies and the benefit of implementation reuse from implementation inheritance?One popular technique is dual hierarchies.There are many ways of implementing the idea of dual hierarchies; here, we use a multiple-inheritance variant.
Capping an individual virtual function with final is error-prone as final can easily be overlooked when defining/overriding a set of functions.Fortunately, the compiler catches such mistakes: You cannot re-declare/re-open a final member in a derived class.
There are examples where final can be important for both logical and performance reasons.One example is a performance-critical AST hierarchy in a compiler or language analysis tool.New derived classes are not added every year and only by library implementers.However, misuses are (or at least have been) far more common.
The result of pb2->id() == "D" is actually implementation defined.We added it to warn of the dangers of home-brew RTTI.This code might work as expected for years, just to fail on a new machine, new compiler, or a new linker that does not unify character literals.
The compiler will flag the uninitialized cm3 because it is a const, but it will not catch the lack of initialization of m3.Usually, a rare spurious member initialization is worth the absence of errors from lack of initialization and often an optimizercan eliminate a redundant initialization (e.g., an initialization that occurs immediately before an assignment).
Use gsl::span instead.Pointers should only refer to single objects.Pointer arithmetic is fragile and easy to get wrong, the source of many, many bad bugs and security violations.span is a bounds-checked, safe type for accessing arrays of data.Access into an array with known bounds using a constant as a subscript can be validated by the compiler.
You have no idea what such code does. Portability.Even if it does something sensible for you, it might do something different on another compiler (e.g., the next release of your compiler) or with a different optimizer setting. 2ff7e9595c
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