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va_copy

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< cpp‎ | utility‎ | variadic

 
 
Utilidades de la biblioteca
Escriba apoyo (basic types, RTTI, type traits)
Gestión de memoria dinámica
Gestión de errores
Programa de servicios públicos
Funciones variadic
Fecha y hora
Objetos Function
initializer_list(C++11)
bitset
hash(C++11)
Operadores relacionales
Original:
Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
Pares y tuplas
Original:
Pairs and tuples
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pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
Cambiar, hacia adelante y mover
Original:
Swap, forward and move
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swap
forward(C++11)
move(C++11)
move_if_noexcept(C++11)
declval(C++11)
 
 
Defined in header <cstdarg>
void va_copy(va_list dest, va_list src);
(desde C++11)
Las copias va_copy macro src a dest .
Original:
The va_copy macro copies src to dest.
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va_end debería llamarse en dest antes de que vuelva función o cualquier posteriores re-inicialización de dest (a través de llamadas a va_start o 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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Contenido

[editar] Parámetros

dest -
una instancia de la va_list escriba inicializar
Original:
an instance of the va_list type to initialize
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src -
va_list la fuente que se utiliza para inicializar dest
Original:
the source va_list that will be used to initialize dest
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[editar] Ampliado valor

(Ninguno)
Original:
(none)
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[editar] Ejemplo

#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';
}

Output:

0.920258

[editar] Ver también

permite el acceso a los argumentos de la función variadic
Original:
enables access to variadic function arguments
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(función macro) [edit]
accede a la función siguiente argumento variadic
Original:
accesses the next variadic function argument
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(función macro) [edit]
termina recorrido de los argumentos de la función variadic
Original:
ends traversal of the variadic function arguments
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(función macro) [edit]