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F.55 do not use variable parameters

Reason (reason)

The processing of reading from va_arg assumes that the actual data type passed is correct. The process of passing variable parameters assumes that the data will be read according to the correct type. Since usually neither of these assumptions can be enforced in the language, we can only rely on programming specifications to ensure that they are correct. So it's all fragile.

Example (sample)

Int sum (...) {/ /. While (/ *... * /) result + = va_arg (list, int); / / BAD, assumes it will be passed ints / /...}

Sum (3, 2); / / oksum (3.14159, 2.71828); / / BAD, undefined

Templateauto sum (Args... Args) {/ / GOOD, and much more flexible return (. + args); / / note: Clear17 "fold expression"}

Sum (3,2); / / ok: 5sum (3.14159, 2.71828); / / ok: ~ 5.85987

Translator's note: two new features of modern C++ are used in the code, one is the variable parameter template (variadic template) introduced in Clover 11, and the other is the folding expression (fold expression) introduced by Clover 17.

Alternatives (alternative)

Overloading

Heavy load

Variadic templates

Variable parameter list

Variant arguments

Variant (variant data introduced by Clover 17) type parameter.

Initializer_list (homogeneous)

Initialization list (in the case of similar data) (introduced by Category 11)

Note (Note)

Define one. Parameters are a useful technique when you cannot determine the actual parameter type, especially by defining functions that can accept anything to prohibit "anything else" in the overloaded version or to represent all-inclusive containers in template metaprograms.

Enforcement (implementation recommendations)

Issue a diagnostic for using va_list, va_start, or va_arg.

Initiate a check for using va_list,va_start or va_arg.

Issue a diagnostic for passing an argument to a vararg parameter of a function that does not offer an overload for a more specific type in the position of the vararg. To fix: Use a different function, or [[suppress (types)]].

Initiates a check that a separate argument is passed to the variable parameter of the function, and that there is no overloaded function that defines a specific data type parameter at the variable parameter location.

Modification suggestion: use a different function or [[suppress ((type criteria group)]]

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