使用 std::experimental::optional，给出编译错误

Using std::experimental::optional giving compilation errors

本文关键字：编译 错误 optional std experimental 使用      更新时间：2023-10-16

我第一次使用可选功能，知道这段代码出了什么问题，我希望从存储在retCode中的元组中检索值

#include <iostream>
#include <experimental/optional>
std::experimental::optional<std::tuple<uint16_t, uint32_t, uint32_t>> addEntity();
std::experimental::optional<std::tuple<uint16_t, uint32_t, uint32_t>> addEntity() {
uint32_t ipR = 1111;
uint32_t ipU = 2222;
uint16_t entityId = 0;
return std::make_tuple(entityId, ipR, ipU);
}

int main()
{
auto retCode =  addEntity();
std::cout<<std::get<0>(retCode)<<std::endl;
return 0;
}

编译错误

g++ experiment.cpp
In file included from /usr/include/c++/7/bits/move.h:54:0,
from /usr/include/c++/7/bits/nested_exception.h:40,
from /usr/include/c++/7/exception:143,
from /usr/include/c++/7/ios:39,
from /usr/include/c++/7/ostream:38,
from /usr/include/c++/7/iostream:39,
from experiment.cpp:1:
/usr/include/c++/7/type_traits: In instantiation of ‘struct std::is_trivially_destructible<std::tuple<short unsigned int, unsigned int, unsigned int> >’:
/usr/include/c++/7/experimental/optional:203:5:   required from ‘class std::experimental::fundamentals_v1::optional<std::tuple<short unsigned int, unsigned int, unsigned int> >’

没有从optional<T>到T的隐式转换，您需要提取值。

int main()
{
auto retCode =  addEntity();
std::cout<<std::get<0>(retCode.value())<<std::endl; // can throw std::bad_optional_access
return 0;
}

除非你有其他地方需要addEntity返回可选元组，而不仅仅是调用addEntity初始化可选元组的地方，否则它应该只返回一个元组。

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