我有三个std :: ofstream对象,我把它们放在像下面这样的函数中,并在main()中使用它们。我编译时收到了很多错误信息,有人可以帮我吗?
#include<string>
#include<tuple>
#include<fstream>
#include<iostream>
std::tuple<std::ofstream, std::ofstream, std::ofstream>
set_ofstream_tuple() {
std::ofstream out1("out1.txt", std::ofstream::out);
out1 << "this is out1.txt" << std::endl;
std::ofstream out2("out2.txt", std::ofstream::out);
out2 << "this is out2.txt" << std::endl;
std::ofstream out3("out3.txt", std::ofstream::out);
out3 << "this is out3.txt" << std::endl;
return std::make_tuple(out1, out2, out3);
}
int main() {
std::ofstream out1, out2, out3;
std::tie(out1, out2, out3) = set_ofstream_tuple();
/// make use of there ofstreams more here
}
答案 0 :(得分:4)
这一行:
return std::make_tuple<out1, out2, out3>;
很奇怪。你想做什么? :)
std::make_tuple
是一个函数,它从参数中生成一个元组:
return std::make_tuple(std::move(out1), std::move(out2), std::move(out3));
请注意std::move
,这些是必需的,因为您无法复制std::ofstream
。
答案 1 :(得分:1)
问题是你在返回之前将不可复制的ofstream
复制到元组中。
一种解决方案是在返回之前将ofstreams移动到元组中:
#include<string>
#include<tuple>
#include<fstream>
#include<iostream>
std::tuple<std::ofstream, std::ofstream, std::ofstream>
set_ofstream_tuple()
{
std::ofstream out1("out1.txt", std::ofstream::out);
out1 << "this is out1.txt" << std::endl;
std::ofstream out2("out2.txt", std::ofstream::out);
out2 << "this is out2.txt" << std::endl;
std::ofstream out3("out3.txt", std::ofstream::out);
out3 << "this is out3.txt" << std::endl;
return std::make_tuple(std::move(out1), std::move(out2), std::move(out3));
}
int main() {
std::ofstream out1, out2, out3;
std::tie(out1, out2, out3) = set_ofstream_tuple();
/// make use of there ofstreams more here
}
证明:on godbolt
另一种解决方案是在创建过程中使用元组作为主存储:
#include<string>
#include<tuple>
#include<fstream>
#include<iostream>
std::tuple<std::ofstream, std::ofstream, std::ofstream>
set_ofstream_tuple()
{
auto streams = std::make_tuple(std::ofstream("out1.txt", std::ofstream::out),
std::ofstream("out2.txt", std::ofstream::out),
std::ofstream("out3.txt", std::ofstream::out));
auto& out1 = std::get<0>(streams);
auto& out2 = std::get<1>(streams);
auto& out3 = std::get<2>(streams);
out1 << "this is out1.txt" << std::endl;
out2 << "this is out2.txt" << std::endl;
out3 << "this is out3.txt" << std::endl;
return streams;
}
int main() {
std::ofstream out1, out2, out3;
std::tie(out1, out2, out3) = set_ofstream_tuple();
/// make use of there ofstreams more here
}
从c ++ 17开始,我们将能够避免使用即将到来的ofstream
(此处使用std::optional
进行演示)重复构建空std::experimental
}:
#include<string>
#include<tuple>
#include<fstream>
#include<iostream>
#include <experimental/optional>
std::tuple<std::ofstream, std::ofstream, std::ofstream>
set_ofstream_tuple()
{
auto streams = std::make_tuple(std::ofstream("out1.txt", std::ofstream::out),
std::ofstream("out2.txt", std::ofstream::out),
std::ofstream("out3.txt", std::ofstream::out));
auto& out1 = std::get<0>(streams);
auto& out2 = std::get<1>(streams);
auto& out3 = std::get<2>(streams);
out1 << "this is out1.txt" << std::endl;
out2 << "this is out2.txt" << std::endl;
out3 << "this is out3.txt" << std::endl;
return streams;
}
int main() {
std::experimental::optional<std::ofstream> out1, out2, out3;
std::tie(out1, out2, out3) = set_ofstream_tuple();
/// make use of there ofstreams more here
}