Variadic functions

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[Bearbeiten] Usage

[Bearbeiten] Standard Konvertierungen

• std::nullptr_t wird void* umgewandelt

  Original:

  std::nullptr_t is converted to void*

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• float Argumente werden double wie in Floating-Point-Förderung umgewandelt

  Original:

  float arguments are converted to double as in Floating-Point-Förderung

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• bool, char, short und ohne Bereichseinschränkung Aufzählungen sind int oder breiter Integer-Typen wie in integer Förderung umgewandelt

  Original:

  bool, char, short, and unscoped enumerations are converted to int or wider integer types as in integer Förderung

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[Bearbeiten] Alternativen

• Variadic Vorlagen können auch verwendet werden, um Funktionen, die variablen Anzahl von Argumenten nehmen zu schaffen. Sie sind oft die bessere Wahl, weil sie nicht durchsetzen, Einschränkungen für die Typen der Argumente, nicht durchführen Integral-und Floating-Point-Aktionen und sind typsicher. (seit C++11)

  Original:

  Variadic templates can also be used to create functions that take variable number of arguments. They are often the better choice because they do not impose restrictions on the types of the arguments, do not perform integral and floating-point promotions, and are type safe. (seit C++11)

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• Wenn alle variable Argumente einen gemeinsamen Typ Aktie bietet ein std::initializer_list einen bequemen Mechanismus (wenn auch mit einer anderen Syntax) für den Zugriff auf variable Argumente .

  Original:

  If all variable arguments share a common type, a std::initializer_list provides a convenient mechanism (albeit with a different syntax) for accessing variable arguments.

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[Bearbeiten] Beispiel

#include <iostream>
#include <cstdarg>
 
void simple_printf(const char *fmt, ...)
{
    va_list args;
    va_start(args, fmt);
 
    while (*fmt != '\0') {
        if (*fmt == 'd') {
            int i = va_arg(args, int);
            std::cout << i << '\n';
        } else if (*fmt == 'c') {
            // note automatic conversion to integral type
            int c = va_arg(args, int);
            std::cout << static_cast<char>(c) << '\n';
        } else if (*fmt == 'f') {
            double d = va_arg(args, double);
            std::cout << d << '\n';
        }
        ++fmt;
    }
 
    va_end(args);
}
 
int main()
{
    simple_printf("dcff", 3, 'a', 1.999, 42.5); 
}

3
a
1.999
42.5