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The Metacode extension to C++ (Vandevoorde 2003) [1] was an early experimental system to allow compile-time function evaluation (CTFE) and code injection as an improved syntax for C++ template metaprogramming. In earlier versions of C++, template metaprogramming is often used to compute values at compile time, such as:
Both the C99 and C++11 standards require at least one argument, but since C++20 this limitation has been lifted through the __VA_OPT__ functional macro. The __VA_OPT__ macro is replaced by its argument when arguments are present, and omitted otherwise. Common compilers also permit passing zero arguments before this addition, however.
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 ...
A function definition starts with the name of the type of value that it returns or void to indicate that it does not return a value. This is followed by the function name, formal arguments in parentheses, and body lines in braces. In C++, a function declared in a class (as non-static) is called a member function or method.
The C date and time functions are a group of functions in the standard library of the C programming language implementing date and time manipulation operations. [1] They provide support for time acquisition, conversion between date formats, and formatted output to strings.
Output and input/output parameters prevent function composition, since the output is stored in variables, rather than in the value of an expression. Thus one must initially declare a variable, and then each step of a chain of functions must be a separate statement. For example, in C++ the following function composition:
C++20 added abbreviated function templates which use auto as a placeholder type in the parameter declaration. [2] A constrained placeholder type allows to put constraints on the automatically deduced return type of a function or a variable. C5: A trailing requires-clause. This form is similar to C2 with one notable exception. A trailing ...
The variadic template feature of C++ was designed by Douglas Gregor and Jaakko Järvi [1] [2] and was later standardized in C++11. Prior to C++11, templates (classes and functions) could only take a fixed number of arguments, which had to be specified when a template was first declared.