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In the C and C++ programming languages, an inline function is one qualified with the keyword inline; this serves two purposes: . It serves as a compiler directive that suggests (but does not require) that the compiler substitute the body of the function inline by performing inline expansion, i.e. by inserting the function code at the address of each function call, thereby saving the overhead ...
Differences between C and C++ linkage and calling conventions can also have subtle implications for code that uses function pointers. Some compilers will produce non-working code if a function pointer declared extern "C" points to a C++ function that is not declared extern "C". [22] For example, the following code:
Some things, like types, templates, and extern inline functions, can be defined in more than one translation unit. For a given entity, each definition must have the same sequence of tokens . Non-extern objects and functions in different translation units are different entities, even if their names and types are the same.
The declaration informs the compiler that a variable by that name and type exists, but the compiler does not need to allocate memory for it since it is allocated elsewhere. The extern keyword means "declare without defining". In other words, it is a way to explicitly declare a variable, or to force a declaration without a definition.
This is also valid in C++. (C++ 98/03 deprecated this usage in favor of anonymous namespaces, but is no longer deprecated in C++ 11.) Also, C++ implicitly treats any const namespace-scope variable as having internal linkage unless it is explicitly declared extern, unlike C. A name's linkage is related to, but distinct from, its scope. The scope ...
The term "function prototype" is particularly used in the context of the programming languages C and C++ where placing forward declarations of functions in header files allows for splitting a program into translation units, i.e. into parts that a compiler can separately translate into object files, to be combined by a linker into an executable ...
extern int array1 []; extern int array2 []; int average1 = calc_average_of_four (array1); int average2 = calc_average_of_four (array2); Note that in this trivial case, the compiler may choose to inline both calls to the function, such that the resulting machine code is identical for both the duplicated and non-duplicated examples above.
In computer programming, a declaration is a language construct specifying identifier properties: it declares a word's (identifier's) meaning. [1] Declarations are most commonly used for functions, variables, constants, and classes, but can also be used for other entities such as enumerations and type definitions. [1]