在尝试使用其他OO语言编程多年之后,我试图学习c++。
我试图为另一个类创建一个包装器类,但是很难弄清楚如何正确地设置它。
例如,具有以下内容...
main.cpp
#include "foo.cpp"
#include <iostream>
int main() {
Foo foo(42);
std::cout << foo.get_barx() << std::endl;
return 0;
}
foo.cpp
#include "bar.cpp"
class Foo {
public:
// I'm trying to declare the member variable `m_bar` here. I
// don't want to be instantiating an instance of Bar yet,
// but I think that might be exactly what's happening.
Bar m_bar;
Foo(int y) {
// Here's where I really want to instantiate an instance of Bar
// and assign it to m_bar.
Bar m_bar(y*2);
}
int get_barx() {
return m_bar.getx();
}
};
bar.cpp
class Bar {
public:
int m_x;
// I seem to need this default constructor for the declaration
// of `m_bar` above, but I don't think that line should be
// calling any constructors.
Bar() { m_x = 21; };
Bar(int x) {
m_x = x;
}
int getx() {
return m_x;
}
};
当我编译并运行它时,我得到21,但我希望是84。我很确定我做的事情根本上是错误的,而且我很确定这与我声明
m_bar
成员的方式有关Foo中的变量,但我不知道完成此操作的正确方法。 最佳答案
main.cpp
#include "foo.cpp"
#include <iostream>
int main()
{
Foo foo(42);
std::cout << foo.get_barx() << std::endl;
return 0;
}
在这里,您应该包含一个 header (例如,将“foo.cpp”重命名为“foo.h”)。通常, header 提供声明,而源(例如.cpp文件)提供定义/实现。
Bar.cpp(再次应为 header )
class Bar
{
public:
int m_x;
// A default constructor is not required, however defining any constructor
// prevents auto generation of the default constructor
Bar(int x) : // This starts the initializer list section
m_x(x)
{
// This is assignment not initialization
// m_x = x;
}
// See the trailing 'const', research const correctness
int getx() const
{
return m_x;
}
};
foo.cpp(再次应为 header )
#include "bar.cpp"
class Foo
{
public:
// Just declaring a `Bar` data member
Bar m_bar;
Foo(int y) :
m_bar(y) // Initialize `Bar` data member using the available constructor
{
// First, this declares a new `Bar` instance which is different than
// the class member, regardless of the fact they are named the same
// Bar m_bar(y*2);
// Furthermore, even if you did the following it is assignment not initialization
// m_bar = Bar(y*2);
// Since initialization already occurred before this point an error
// will result if the `Bar` data member isn't instantiated via the
// only available constructor, since there isn't a default constructor as
// explained above
}
// Same comment about const correctness
int get_barx() const
{
return m_bar.getx();
}
};
关于c++ - 如何包装另一个类(C++),我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/32833774/