Defined Terms

catch-all A catch clause in which the exception declaration is (...). A catch-all clause catches an exception of any type. It is typically used to catch an exception that is detected locally in order to do local cleanup. The exception is then rethrown to another part of the program to deal with the underlying cause of the problem.

catch clause Part of the program that handles an exception. A catch clause consists of the keyword catch followed by an exception declaration and a block of statements. The code inside a catch does whatever is necessary to handle an exception of the type defined in its exception declaration.

constructor order Under nonvirtual inheritance, base classes are constructed in the order in which they are named in the class derivation list. Under virtual inheritance, the virtual base class(es) are constructed before any other bases. They are constructed in the order in which they appear in the derivation list of the derived type. Only the most derived type may initialize a virtual base; constructor initializers for that base that appear in the intermediate base classes are ignored.

exception declaration catch clause declaration that specifies the type of exception that the catch can handle. The declaration acts like a parameter list, whose single parameter is initialized by the exception object. If the exception specifier is a nonreference type, then the exception object is copied to the catch.

exception handling Language-level support for managing run-time anomalies. One independently developed section of code can detect and “raise” an exception that another independently developed part of the program can “handle.” The error-detecting part of the program throws an exception; the error-handling part handles the exception in a catch clause of a try block.

exception object Object used to communicate between the throw and catch sides of an exception. The object is created at the point of the throw and is a copy of the thrown expression. The exception object exists until the last handler for the exception completes. The type of the object is the static type of the thrown expression.

file static Name local to a file that is declared with the static keyword. In C and pre-Standard versions of C++, file statics were used to declare objects that could be used in a single file only. File statics are deprecated in C++, having been superseded by the use of unnamed namespaces.

function try block Used to catch exceptions from a constructor initializer. The keyword try appears before the colon that starts the constructor initializer list (or before the open curly of the constructor body if the initizlier list is empty) and closes with one or more catch clauses that appear after the close curly of the constructor body.

global namespace The (implicit) namespace in each program that holds all global definitions.

handler Synonym for a catch clause.

inline namespace Members of a namespace designated as inline can be used as if they were members of an enclosing namespace.

multiple inheritance Class with more than one direct base class. The derived class inherits the members of all its base classes. A separate access specifier may be provided for each base class.

namespace Mechanism for gathering all the names defined by a library or other collection of programs into a single scope. Unlike other scopes in C++, a namespace scope may be defined in several parts. The namepsace may be opened and closed and reopened again in disparate parts of the program.

namespace alias Mechanism for defining a synonym for a given namespace:

namespace N1 = N;

defines N1 as another name for the namespace named N. A namespace can have multiple aliases; the namespace name or any of its aliases may be used interchangeably.

namespace pollution Occurs when all the names of classes and functions are placed in the global namespace. Large programs that use code written by multiple independent parties often encounter collisions among names if these names are global.

noexcept operator Operator that returns a bool indicating whether a given expression might throw an exception. The expression is unevaluated. The result is a constant expression. Its value is true if the expression does not contain a throw and calls only functions designated as nonthrowing; otherwise the result is false.

noexcept specification Keyword used to indicate whether a function throws. When noexcept follows a function’s parameter list, it may be optionally followed by a parenthesized constant expression that must be convertible to bool. If the expression is omitted, or if it is true, the function throws no exceptions. An expression that is false or a function that has no exception specification may throw any exception.

nonthrowing specification An exception specification that promises that a function won’t throw. If a nonthrowing functions does throw, terminate is called. Nonthrowing specifiers are noexcept without an argument or with an argument that evaluates as true and throw().

raise Often used as a synonym for throw. C++ programmers speak of “throwing” or “raising” an exception interchangably.

rethrow A throw that does not specify an expression. A rethrow is valid only from inside a catch clause, or in a function called directly or indirectly from a catch. Its effect is to rethrow the exception object that it received.

stack unwinding The process whereby the functions are exited in the search for a catch. Local objects constructed before the exception are destroyed before entering the corresponding catch.

terminate Library function that is called if an exception is not caught or if an exception occurs while a handler is in process. terminate ends the program.

throw e Expression that interrupts the current execution path. Each throw transfers control to the nearest enclosing catch clause that can handle the type of exception that is thrown. The expression e is copied into the exception object.

try block Block of statements enclosed by the keyword try and one or more catch clauses. If the code inside the try block raises an exception and one of the catch clauses matches the type of the exception, then the exception is handled by that catch. Otherwise, the exception is passed out of the try to a catch further up the call chain.

unnamed namespace Namespace that is defined without a name. Names defined in an unnamed namespace may be accessed directly without use of the scope operator. Each file has its own unique unnamed namespace. Names in an unnamed namespace are not visible outside that file.

using declaration Mechanism to inject a single name from a namespace into the current scope:

using std::cout;

makes the name cout from the namespace std available in the current scope. The name cout can subseuquently be used without the std:: qualifier.

using directive Declaration of the form

using NS;

makes all the names in the namespace named NS available in the nearest scope containing both the using directive and the namespace itself.

virtual base class Base class that specifies virtual in its own derivation list. A virtual base part occurs only once in a derived object even if the same class appears as a virtual base more than once in the hierarchy. In nonvirtual inheritance a constructor may initialize only its direct base class(es). When a class is inherited virtually, that class is initialized by the most derived class, which therefore should include an initializer for all of its virtual parent(s).

virtual inheritance Form of multiple inheritance in which derived classes share a single copy of a base that is included in the hierarchy more than once.

:: operator Scope operator. Used to access names from a namespace or a class.