If decl-specifier-seq of the function declaration contains the auto keyword, the end return type can be omitted and the compiler derives from the expression type used in the return statement. If the return type does not use decltype(auto), the deduction follows the rules of model argument deduction: In general, a function is a “subroutine” that can be called by external (or internal if recursive) code of the function. Like the program itself, a function consists of a sequence of instructions called function bodies. Values can be passed to a function, and the function returns a value. A non-member function definition can appear only at the namespace level (there are no nested functions). A member function definition can also appear in the body of a class definition. They have the following syntax: If instead of a function body the special syntax = delete; is used, the function is set as deleted. Any use of a deleted function is defective (the program does not compile). These include explicit (using a function call operator) and implicit (a call to a deleted overloaded operator, a special member function, a mapping function, and so on), creating a pointer or pointer to a deleted function, and even using a deleted function in an expression that is not potentially evaluated.
However, implicit ODR use of a non-pure virtual member function that is randomly removed is allowed. You can also specify a default value for an ellipse. This value is used as the value for all arguments that are intentionally omitted. In the following, the deleted definition of a function must be the first declaration of a translation unit: A previously declared function cannot be redeclared as deleted: You can write functions that take a variable number of parameters by entering the special parameter “… ” (called ellipse) in the function definition. For example, here is a function that returns the sum of all its arguments, regardless of their number: Function declaration of a function named multiply: A function is provided by the user if it was declared by the user and was not explicitly set as the default or suppressed in its initial declaration. An explicit default function provided by the user (that is, explicitly after the first declaration) is defined at the point where it is explicitly predefined. If such a function is implicitly defined as suppressed, the program is malformed. Declaring a function as a standard function after its initial declaration can enable efficient execution and precise definition, while providing a stable binary interface to an evolving code base. As with any declaration, the func function type declared as ret func(params) is ret(params) (except for the rewritten parameter type described below): see Type name. A safer way to conditionally define functions is to assign a function expression to a variable: New declarations or specializations of functions or function templates that use return type deduction must use the same placeholders for the return type: Note the difference between parameters and arguments: name is the name of a local variable used during a function call with the corresponding real argument initialized. (See § 6.6.1, page , for a discussion of local variables.) As in most programming languages, real arguments correspond to formal parameters from left to right: a function expression is similar to a function declaration and has the same syntax as the latter (see function expression for details).
A function expression can be part of a larger expression. You can define “named” function expressions (where the name of the expression can be used, for example, in the call stack) or “anonymous” function expressions. Function expressions are not elevated to the top of the pane and therefore cannot be used before they appear in code. However, the attributes that appear after the declarator (in the syntax above) apply to the function type, not to the function itself: One of the advantages of creating a named function expression is that in the event of an error, the stack trace includes the name of the function, making it easier to find the origin of the error. If the function is overloaded, the overload resolution occurs first, and the program is defective only if the deleted function is selected: a function declaration introduces the name of the function and its type. A function definition maps the function name/type to the function body. Although top-level resume qualifiers for parameters are removed from function declarations, they change the type of parameter as it is visible in the body of a function: Note: Using the Function constructor to create functions is not recommended because the function text is required as a string. This can prevent some JS engine optimizations and cause other problems. the most common species; They pass values to functions. Depending on the programming language, input parameters can be passed in different ways (e.g., value call, address call, reference call). The name of an argument.
NULL arguments must be specified with (). Parentheses are not required for a single argument. (as foo = > 1) Virtual functions and coroutines (since C++20) cannot use the return type derivation: as mentioned in declarations, the declarer can be followed by a requires clause that declares the constraints associated with the function that must be met for the function to be selected by overload resolution.