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va_copy

De cppreference.com
< cpp‎ | utility‎ | variadic

Defined in header <cstdarg>
void va_copy(va_list dest, va_list src);
(depuis C++11)
Les copies va_copy macro src à dest .
Original:
The va_copy macro copies src to dest.
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va_end doit être appelée sur dest avant le retour de fonction ou une suite de ré-initialisation de dest (via des appels à va_start ou va_copy) .
Original:
va_end should be called on dest before the function returns or any subsequent re-initialization of dest (via calls to va_start or va_copy).
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Sommaire

[modifier] Paramètres

dest -
une instance de la va_list taper à initialiser
Original:
an instance of the va_list type to initialize
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src -
la va_list source qui sera utilisé pour initialiser dest
Original:
the source va_list that will be used to initialize dest
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[modifier] Élargi valeur

(Aucun)
Original:
(none)
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[modifier] Exemple

#include <iostream>
#include <cstdarg>
#include <cmath>
 
double sample_stddev(int count, ...) 
{
    double sum = 0;
    va_list args1;
    va_start(args1, count);
    va_list args2;
    va_copy(args2, args1);
    for (int i = 0; i < count; ++i) {
        double num = va_arg(args1, double);
        sum += num;
    }
    double mean = sum / count;
 
    double sum_sq_diff = 0;
    for (int i = 0; i < count; ++i) {
        double num = va_arg(args2, double);
        sum_sq_diff += (num-mean) * (num-mean);
    }
    return std::sqrt(sum_sq_diff / count);
}
 
int main() 
{
    std::cout << sample_stddev(4, 25.0, 27.3, 26.9, 25.7) << '\n';
}

Résultat :

0.920258

[modifier] Voir aussi

permet d'accéder aux arguments de la fonction variadique
Original:
enables access to variadic function arguments
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(fonction macro) [edit]
accède à l'argument de la fonction suivante variadique
Original:
accesses the next variadic function argument
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(fonction macro) [edit]
termine la traversée des arguments de la fonction variadique
Original:
ends traversal of the variadic function arguments
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(fonction macro) [edit]