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va_copy

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< cpp‎ | utility‎ | variadic

 
 
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Gerenciamento de memória dinâmica
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Utilidades do programa
Variadic funções
Data e hora
Objetos de função
initializer_list(C++11)
bitset
hash(C++11)
Os operadores relacionais
Original:
Relational operators
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rel_ops::operator!=
rel_ops::operator>
rel_ops::operator<=
rel_ops::operator>=
Pares e tuplas
Original:
Pairs and tuples
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pair
tuple(C++11)
piecewise_construct_t(C++11)
piecewise_construct(C++11)
Troque, avançar e avançar
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);
(a partir do C++ 11)
As cópias va_copy macro src para dest.
Original:
The va_copy macro copies src to dest.
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va_end deve ser chamado em dest antes do retorno de função ou qualquer subseqüentes re-inicialização do dest (via chamadas para 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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Índice

[editar] Parâmetros

dest -
uma instância do tipo va_list para inicializar
Original:
an instance of the va_list type to initialize
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src -
o va_list fonte que será usado para inicializar dest
Original:
the source va_list that will be used to initialize dest
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[editar] Expandiu valor

(Nenhum)
Original:
(none)
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[editar] Exemplo

#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] Veja também

permite o acesso a argumentos de função variádicos
Original:
enables access to variadic function arguments
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(função macro) [edit]
acessa o argumento da função próximo aridade
Original:
accesses the next variadic function argument
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(função macro) [edit]
termina travessia dos argumentos da função variádicos
Original:
ends traversal of the variadic function arguments
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(função macro) [edit]