返回STL映射对象 [英] Returning a STL Map Object

问题描述

我是一个STL新手试图建立一个DUTBus类，它有一张地图

对象。在我的成员函数中，我尝试返回一个Map对象，但是，

它似乎不起作用。我指的是Bus getBus（）

函数。


我需要这样做，因为要添加设备引脚（通过

registerPin（）函数。换句话说，我需要通过在对象中插入新的（键，值）对来修改地图。

。但是，当我试图通过返回它来获取总线对象时，它不起作用！


请帮忙！


谢谢

Anand


#include< string>

typedef map< int，string> Bus;

typedef Bus :: iterator BusIterator;


class DUTBus

{

private：

Bus _bus;

public：

DUTBus（）{}

Bus getBus（）;

inline int getBusSize（）{return（_bus.size（））;}

void registerPin（int，string）;


};

巴士DUTBus :: getBus（）

{

返回（_bus）;

}


void DUTBus :: registerPin（int _idx，string _pin）

{

Bus myBus = this-> getBus（）;

BusIterator iter;

iter = myBus .begin（）;

myBus.insert（pair< int，string>（_ idx，_pin））;

cout<< Inserted Bus [" << _idx<< "] \t = \t" << _pin;

}


main（无效）

{

巴士myBus ;

DUTBus * DataBus = new DUTBus（）;

DataBus-> registerPin（1，" T_x_p_ad1"）;

DataBus- > registerPin（2，" T_x_p_ad2"）;

DataBus-> registerPin（3，" T_x_p_ad3"）;


myBus = DataBus- > getBus（）;

cout<< 这辆公共汽车的大小为 << myBus.getBusSize（）<< endl;

}

[见 http://www.gotw.ca/resources/clcm.htm 了解有关的信息]

[comp.lang.c ++。moderated。第一次海报：做到这一点！ ]

I am an STL newbie trying to build a class DUTBus that has a map
object. In my member function, I try to return a Map Object, however,
it does not seem to work. I am referring to "Bus getBus()"
function.

I need to do this because in order to "add" device pins (via
registerPin() function. In other words, I need to modify the map by
inserting new (key,value) pairs into the object. However, when I try to
access the bus object by returning it, it doesnt work!

Please help!

Thanks
Anand

#include <string>
typedef map<int, string> Bus;
typedef Bus::iterator BusIterator;

class DUTBus
{
private:
Bus _bus;
public:
DUTBus() { }
Bus getBus();
inline int getBusSize() { return (_bus.size()); }
void registerPin(int, string);

};
Bus DUTBus::getBus()
{
return(_bus);
}

void DUTBus::registerPin(int _idx, string _pin)
{
Bus myBus = this->getBus();
BusIterator iter;
iter = myBus.begin();
myBus.insert(pair<int, string>(_idx,_pin));
cout << "Inserted Bus[" << _idx << "]\t=\t" << _pin;
}


main(void)
{
Bus myBus;
DUTBus* DataBus = new DUTBus();
DataBus->registerPin(1,"T_x_p_ad1");
DataBus->registerPin(2,"T_x_p_ad2");
DataBus->registerPin(3,"T_x_p_ad3");

myBus = DataBus->getBus();
cout << "This bus has a size of " << myBus.getBusSize() << endl;
}
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

推荐答案

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"anand" <wr********@gmail.com> wrote in message
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我是一个STL新手试图建立一个具有地图对象的DUTBus类。在我的成员函数中，我尝试返回一个Map对象，但是，它似乎不起作用。我指的是Bus getBus（）功能。

我需要这样做，因为要添加。设备引脚（通过
registerPin（）函数。换句话说，我需要通过在对象中插入新的（键，值）对来修改地图。但是，当我尝试
时通过返回来访问公共汽车对象，它不起作用！

请帮助！

感谢
Anand

#include< string> ;
typedef map< int，string> Bus;
typedef Bus :: iterator BusIterator;

class DUTBus
{
私人：
总线_bus;
注意：标识符名称中最好避免使用前导下划线

（它们在某些情况下保留用于实现）。

尾随下划线（bus_）因此通常是首选。

public：
DUTBus（）{}
Bus getBus（）;
问题：在C ++中，这会返回（深层）副本存储的_bus

对象。如果要返回对象引用，则需要

明确地这样做：

Bus& getBus（） {return _bus;}

Howe ver，后者违背了拥有私人

数据成员的目的，因此最好避免使用。

一个有时有用的替代方案，它仍然允许班级

控制其不变量，是：

Bus const& getBus（）const {return _bus; } $ / $
inline int getBusSize（）{return（_bus.size（））; }
注意：内联在这里是多余的，''const''会更好：

int getBusSize（）const {return（_bus.size（））; }

void registerPin（int，string）;

};

Bus DUTBus :: getBus（）
{
return（_bus）;
}

void DUTBus :: registerPin（int _idx，string _pin）同样，最好避免使用前导下划线。在这种情况下使用它们是一种非常罕见的C ++风格。

{
Bus myBus = this-> getBus（）;
这将创建_bus对象的本地副本。然后修改并销毁本地

副本，而_bus数据

成员保持不变。 ***这就是导致你的''bug'的原因'***

直接使用_bus数据成员。或者，如果您想要对数据成员进行本地

引用，请使用：

Bus& myBus = _bus;

BusIterator iter;
iter = myBus.begin（）;
首选组合声明和实例：

BusIterator const iter = myBus.begin（）;

但无论如何，此函数不需要''iter'' 。

myBus.insert（pair< int，string>（_ idx，_pin））;
cout<< Inserted Bus [" << _idx<< "] \t = \t" << _pin;
}
如果用以下内容替换它的主体，该函数将正常工作：

_bus.insert（pair< int，string>（_ idx，_pin））;

甚至更容易，因为你似乎并不关心一个已经存在相同数字的销钉

：

_bus [_idx] = _pin;

main（无效）
{
巴士myBus;
最好在首次使用时声明局部变量... DUTBus * DataBus = new DUTBus（）;
除非有必要，否则不要在堆上分配对象。只需使用：

DUTBus DataBus; DataBus-> registerPin（1，T_x_p_ad1）;
DataBus-> registerPin（2，T_x_p_ad2）;
DataBus-> registerPin（3，T_x_p_ad3）;

myBus = DataBus-> getBus（）;
这又创建了一个DataBus-> _bus的本地*副本*，其中
可能不是您想要的（尽管在这种情况下它可以正常工作）。

cout<< 这辆公共汽车的大小为 << myBus.getBusSize（）<< endl;
}

I am an STL newbie trying to build a class DUTBus that has a map
object. In my member function, I try to return a Map Object, however,
it does not seem to work. I am referring to "Bus getBus()"
function.

I need to do this because in order to "add" device pins (via
registerPin() function. In other words, I need to modify the map by
inserting new (key,value) pairs into the object. However, when I try to
access the bus object by returning it, it doesnt work!

Please help!

Thanks
Anand

#include <string>
typedef map<int, string> Bus;
typedef Bus::iterator BusIterator;

class DUTBus
{
private:
Bus _bus; NB: Leading underscores are best avoided in identifier names
(they are reserved for the implementation in some contexts).
Trailing underscores (bus_) are therefore usually preferred.
public:
DUTBus() { }
Bus getBus(); Problem: In C++, this returns a (deep) copy of the stored _bus
object. If you want to return an object reference, you need to
do so explicitly:
Bus& getBus() { return _bus; }
However, the latter defeats the purpose of having a private
data member, and is therefore best avoided.
A sometimes useful alternative, which still allows the class to
control its invariants, is:
Bus const& getBus() const { return _bus; }
inline int getBusSize() { return (_bus.size()); } NB: inline is redundant here, and a ''const'' would be better:
int getBusSize() const { return (_bus.size()); }
void registerPin(int, string);

};
Bus DUTBus::getBus()
{
return(_bus);
}

void DUTBus::registerPin(int _idx, string _pin)Again, leading underscores are best avoided. And it is
a quite uncommon C++ style to use them in this context.
{
Bus myBus = this->getBus(); This creates a local copy of the _bus object. That local
copy is then modified, and destroyed, while the _bus data
member remains unchanged. ***this is what causes your ''bug''***
Use the _bus data member direcly. Or if you want a local
reference to the data member, use:
Bus& myBus = _bus;
BusIterator iter;
iter = myBus.begin(); Prefer combining declaration and instanciation:
BusIterator const iter = myBus.begin();
But anyway, ''iter'' is not needed in this function.
myBus.insert(pair<int, string>(_idx,_pin));
cout << "Inserted Bus[" << _idx << "]\t=\t" << _pin;
} The function will work correctly if you replace its body with:
_bus.insert( pair<int, string>(_idx,_pin) );
Or even easier, since you don''t seem to care about wheter a pin
with the same number already existed:
_bus[_idx] = _pin;
main(void)
{
Bus myBus; It is better to declare local variables on first use... DUTBus* DataBus = new DUTBus(); Don''t allocate objects on the heap unless it is necessary. Just use:
DUTBus DataBus; DataBus->registerPin(1,"T_x_p_ad1");
DataBus->registerPin(2,"T_x_p_ad2");
DataBus->registerPin(3,"T_x_p_ad3");

myBus = DataBus->getBus(); This again creates a local *copy* of the DataBus->_bus , which
may not be what you want (although it will work ok in this context).
cout << "This bus has a size of " << myBus.getBusSize() << endl;
}

我希望这会有所帮助。请注意，在尝试编写更复杂的程序之前，花更多时间学习C ++可能是个好主意...

问候，Ivan

-
http://ivan.vecerina.com/ contact /？subject = NG_POST < - 电子邮件联系表格

Brainbench MVP for C ++<> http://www.brainbench.com


[见 http://www.gotw.ca/resources /clcm.htm 有关的信息]

[comp.lang.c ++。moderated。第一次海报：做到这一点！ ]

I hope this helps. Note that it might be a good idea to spend more time
studying C++ before trying to write more complex programs...
Regards, Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form
Brainbench MVP for C++ <> http://www.brainbench.com


[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

你让一辆公共汽车与DUTBus混淆，插入不能工作

因为你' '插入_bus的本地副本，而不是_bus本身。

另外，不要忘记包含必需的标题并有资格获得

std命名空间：


#include< iostream>

#include< map>

#include< utility>

#include< string>


typedef std :: map< int，std :: string>公共汽车;

typedef Bus :: iterator BusIterator;


class DUTBus

{

private：

Bus _bus;

public：

Bus getBus（）;

inline int getBusSize（）{return（ _bus.size（））; } $ / $
void registerPin（int，std :: string）;

};


Bus DUTBus :: getBus（）

{

返回（_bus）;

}


void DUTBus :: registerPin（int _idx ，std :: string _pin）

{

_bus.insert（std :: pair< int，std :: string>（_ idx，_pin））;

std :: cout<< Inserted Bus [" << _idx<< "] \t = \t" << _pin;

}


int main（无效）

{

巴士myBus;

DUTBus * DataBus = new DUTBus（）;


DataBus-> registerPin（1，" T_x_p_ad1"）;

DataBus - > registerPin（2，" T_x_p_ad2"）;

DataBus-> registerPin（3，" T_x_p_ad3"）;


myBus = DataBus - > getBus（）;

std :: cout<< 这辆公共汽车的大小为 << myBus.size（）<< std :: endl;

}

[见 http://www.gotw.ca/resources/clcm.htm 有关的信息]

[comp.lang.c ++。moderated。第一次海报：做到这一点！ ]

You''re confusing a Bus with a DUTBus, and the insertions don''t work
because you''re inserting into a local copy of _bus, not _bus itself.
Also, don''t forget to include the requisite headers and qualify for the
std namespace:

#include <iostream>
#include <map>
#include <utility>
#include <string>

typedef std::map<int, std::string> Bus;
typedef Bus::iterator BusIterator;

class DUTBus
{
private:
Bus _bus;
public:
Bus getBus();
inline int getBusSize() { return (_bus.size()); }
void registerPin(int, std::string);
};

Bus DUTBus::getBus()
{
return(_bus);
}

void DUTBus::registerPin(int _idx, std::string _pin)
{
_bus.insert(std::pair<int, std::string>(_idx,_pin));
std::cout << "Inserted Bus[" << _idx << "]\t=\t" << _pin;
}

int main(void)
{
Bus myBus;
DUTBus* DataBus = new DUTBus();

DataBus->registerPin(1,"T_x_p_ad1");
DataBus->registerPin(2,"T_x_p_ad2");
DataBus->registerPin(3,"T_x_p_ad3");

myBus = DataBus->getBus();
std::cout << "This bus has a size of " << myBus.size() << std::endl;
}
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

>我尝试返回一个Map对象，然而，它似乎不起作用。

你能不能更具体地说明什么不起作用？

编译时间错误？意外的运行时行为？


据我所知，上述代码唯一不对的是

行：

cout<< 这辆公共汽车的大小为 << myBus.getBusSize（）<< endl;

..你在Bus类型的对象上调用getBusSize（）。类型总线是

实际上是一个地图< int，string>当然，没有会员

函数getBusSize（）。

[见 http://www.gotw.ca/resources/clcm.htm 有关的信息]

[comp.lang .C ++。主持。第一次海报：做到这一点！ ]

> I try to return a Map Object, however, it does not seem to work.
Could you please be a bit more specific about what doesn''t work?
Compile time error? Unexpected runtime behavior?

As far as I can tell the only thing wrong with the above code is the
line:
cout << "This bus has a size of " << myBus.getBusSize() << endl;
.. You are calling getBusSize() on an object of type Bus. Type Bus is
really a map<int, string> and, of course, does not have a member
function getBusSize().
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

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