在构造函数中初始化priority_queue [英] Initializing priority_queue in constructor
问题描述
大家好，
经过多年的C，我以为我最近会转向C ++。我认为
因为我认为在C中，我会对某些事情产生误解。
我创建了一个类foo，其中包含一个私有变量是一个
优先级队列。在类foo的头文件中，我将其声明为：
class foo {
private：
unsigned int count ;
priority_queue< double，std :: vector< double>，更大< double
pqueue;
};
在构造函数中，我被警告我应该在
成员初始化列表中初始化（因为我是新的，我将所有这些警告添加到
我的编译器）。所以，我知道我能做到：
foo :: foo（）
：count（0）
{
}
但现在我被卡住了。如何初始化优先级队列？我希望
拥有一个没有任何东西的优先级队列（即空），并且已经在声明中为我完成了
（我认为......） 。我是否只是通过打开警告来解决问题，我应该忽略
这个关于初始化pqueue的问题？显然，这不是一个错误
我可以继续...但我想知道我该怎么做...
谢谢！
Ray
Hi all,
After many years of C, I thought I''d move to C++ recently. I think
because I think in C, I''m coming to a misunderstanding of something.
I''ve created a class foo which contains a private variable which is a
priority queue. In class foo''s header file, I declared it as:
class foo {
private:
unsigned int count;
priority_queue<double, std::vector<double>, greater<double
pqueue;
};
In the constructor, I''m being warned that I should initialize in the
member initialization list (as I am new, I added all these warnings to
my compiler). So, I know I could do:
foo::foo ()
: count (0)
{
}
but now I''m stuck. How does one initialize a priority queue? I want
to have a priority queue with nothing (i.e., empty) and it''s already
done that for me in the declaration (I think...). Did I just get
myself in trouble by turning on the warnings and I should just ignore
this one about initializing pqueue? Obviously, this isn''t an error
and I can continue...but I would like to know what should I do...
Thanks!
Ray
推荐答案
你好Alf，
感谢您的回复！对不起，但我忘了澄清它确实
编译得很好......但是由于警告标志我正在使用（-Weffc ++
in g ++），I '得到警告（而不是编译错误）。因为我是新的b $ b，我想知道是否要忽略这个警告（即，
什么是最佳做法）。根据我的手册页，-Weffc ++确实如此
这个：
-Weffc ++（仅限C ++）
警告违反以下风格指南
来自Scott
Meyers的'有效C ++书：
*项目11：定义一个复制构造函数和一个分配
运算符
用于具有动态分配内存的类。
*项目12：首选初始化为
施工人员。
....
我把剩下的休息了，因为它似乎很明显是警告我因为
项目12.警告（我用你发布的代码获得
以下......谢谢你把它放在一起！）是：
foo.c：在构造函数''foo :: foo（）''中：
foo.c：16：警告：''foo :: pqueue''应该被初始化在会员中
初始化列表
所以，我想我想知道的是一个priority_queue（矢量等）
被初始化为了满足这个编译器警告或者我应该只是忽略它吗？
谢谢！
Ray
4月26日晚9:18，Alf P. Steinbach < al ... @ start.nowrote：
Hi Alf,
Thank you for your reply! Sorry, but I forgot to clarify that it does
compile fine... But because of the warning flag I''m using (-Weffc++
in g++), I''m getting a warning (and not a compiling error). As I''m
new, I''d like to know whether or not to ignore this warning (i.e.,
what is "best" practice). According to my man pages, -Weffc++ does
this:
-Weffc++ (C++ only)
Warn about violations of the following style guidelines
from Scott
Meyers'' Effective C++ book:
* Item 11: Define a copy constructor and an assignment
operator
for classes with dynamically allocated memory.
* Item 12: Prefer initialization to assignment in
constructors.
....
I cut the rest out as it seems obvious it is warning me because of
Item 12. The warning (which I do get with the code you posted
below...thank you for putting it together!) is:
foo.c: In constructor ''foo::foo()'':
foo.c:16: warning: ''foo::pqueue'' should be initialized in the member
initialization list
So, I guess what I am wondering is can a priority_queue (vector, etc.)
be "initialized" to satisfy this compiler warning or should I just
ignore it?
Thank you!
Ray
On Apr 26, 9:18 pm, "Alf P. Steinbach" <al...@start.nowrote:
发布最小的完整示例是个好主意。
因为它是不可能说出你做错了什么。
以下编译好：
< ;代码>
#include< iostream>
#include< queue>
#include< vector>
使用命名空间std;
class foo {
private：
unsigned int count;
priority_queue< double，std :: vector< double>，more< double pqueue;
public：
foo（）;
< br $>
};
foo :: foo（）
：count（0）
{< br $>
}
int main（）
{
foo o;}
< / code>
It''s a good idea to post a minimal complete example.
As it is it''s impossible to say what you''re doing wrong.
The following compiles fine:
<code>
#include <iostream>
#include <queue>
#include <vector>
using namespace std;
class foo {
private:
unsigned int count;
priority_queue<double, std::vector<double>, greater<double pqueue;
public:
foo();
};
foo::foo ()
: count (0)
{
}
int main()
{
foo o;}
</code>
很抱歉，但忘记添加我使用的是g ++ 4.1.2版（不确定
如果这很重要的话）...
Ray
4月26日晚上9:50，Ray< rayky .. 。@ gmail.comwrote：
Sorry, but forgot to add that I am using g++ version 4.1.2 (not sure
if this matters)...
Ray
On Apr 26, 9:50 pm, Ray <rayky...@gmail.comwrote:
编译好......但由于我正在使用的警告标志（-Weffc ++
in g ++），我收到警告（而不是编译错误）。因为我是新的b $ b，我想知道是否要忽略这个警告（即，
什么是最佳做法）。根据我的手册页，-Weffc ++确实
这个：
compile fine... But because of the warning flag I''m using (-Weffc++
in g++), I''m getting a warning (and not a compiling error). As I''m
new, I''d like to know whether or not to ignore this warning (i.e.,
what is "best" practice). According to my man pages, -Weffc++ does
this:
Ray写道：
[snip]
Ray wrote:
[snip]
我创建了一个包含私有变量的类foo，这是一个
优先队列。在类foo的头文件中，我将其声明为：
class foo {
private：
unsigned int count ;
priority_queue< double，std :: vector< double>，更大< double
pqueue;
};
在构造函数中，我被警告我应该在
成员初始化列表中初始化（因为我是新的，我将所有这些警告添加到
我的编译器）。所以，我知道我能做到：
foo :: foo（）
：count（0）
{
}
但现在我被卡住了。如何初始化优先级队列？我希望
拥有一个没有任何东西的优先级队列（即空），并且已经在声明中为我完成了
（我认为......） 。我刚收到
I''ve created a class foo which contains a private variable which is a
priority queue. In class foo''s header file, I declared it as:
class foo {
private:
unsigned int count;
priority_queue<double, std::vector<double>, greater<double
pqueue;
};
In the constructor, I''m being warned that I should initialize in the
member initialization list (as I am new, I added all these warnings to
my compiler). So, I know I could do:
foo::foo ()
: count (0)
{
}
but now I''m stuck. How does one initialize a priority queue? I want
to have a priority queue with nothing (i.e., empty) and it''s already
done that for me in the declaration (I think...). Did I just get
[snip]
你试过吗：
foo :: foo（）
：pqueue（），
count（0）
{
}
警告只是意味着你应该在进入构造函数体之前初始化每个成员
变量。我只是谨慎使用C ++
，所以我希望上面的代码是正确的。我试图用/ b $ b做的代码是在
实际进入构造函数体之前调用priority_queue默认构造函数。
克里斯
[snip]
Have you tried:
foo::foo ()
: pqueue(),
count(0)
{
}
The warning just meant that you should initialized each of the member
variables before entering the constructor body. I only used C++
sparingly, so I hope the code above is correct. What I was trying to
do with the code was to call priority_queue default constructor before
actually entering the constructor body.
Chris
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