将流的实例插入到容器

Insert instance of ofstream to container

本文关键字：插入 实例      更新时间：2023-10-16

我创建了一个类file，它是std::ofstream的包装器。我创建了一个Container来包含file的所有实例。

class file
{
private:
std::ofstream ofs;
public:
void open(std::string filename);
void write(std::string s);
void close();
};
class Container
{
private:
std::map<int, file> m;

public:
void insert(file f,int i)
{
m.insert(std::pair<int,file> (i,f));
}
void get(int i)
{
m.at(i);
}
};

但是，此代码中存在一个问题。在insert方法中，我正在尝试复制一个无法完成std::pair<int,file>，因为std::ofstream的复制构造函数被删除(请参阅下面的编译错误)。

我想在容器中连续添加file实例。我该怎么做？

这是编译错误

In file included from src/test.cpp:1:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/iostream:38:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/ios:216:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:439:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/algorithm:627:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/utility:274:23: error: call to implicitly-deleted copy constructor of
'file'
: first(__x), second(__y) {}
^      ~~~
src/test.cpp:35:22: note: in instantiation of member function 'std::__1::pair<int, file>::pair' requested here
m.insert(std::pair<int,file> (i,f));
^
src/test.cpp:9:21: note: copy constructor of 'file' is implicitly deleted because field 'ofs' has a deleted copy constructor
std::ofstream ofs;
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/fstream:1168:5: note: copy constructor is implicitly deleted because
'basic_ofstream<char, std::__1::char_traits<char> >' has a user-declared move constructor
basic_ofstream(basic_ofstream&& __rhs);
^
1 error generated.

如果你想用file初始化你的Container而不复制它们，那么你可以依靠std::ofstream的移动构造函数：

void insert(file &&f, int i)
{
m.insert(std::pair<int,file>(i, std::move(f)));
}

然后，您将执行以下操作：

cont.insert(file{}, 0); // Construct a file when inserting, you already have an rvalue

或：

file myfile;
myfile.open(...); // Do whatever you want with myfile...
cont.insert(std::move(myfile), 0); // And then move it, as long as you are not using if after

如果您的file不可移动构造，则可以就地构造它：

template <typename... Args>
void insert(int i, Args&&... args) {
m.emplace(std::piecewise_construct, std::tuple<int>(i),
std::tuple<Args>(std::forward<Args>(args)...));
}

此外，如果要插入默认初始化的文件(如第一个示例所示)，只需执行以下操作：

void insert(int i)
{
m[i];
}
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