初始化而不分配 [英] Initializing without assigning
问题描述
来自写作主要是用Java编写的，我很难理解如何在没有初始化的情况下声明一个成员，并且稍后再这样做......在Java中，
我会写类似
public static void main（String [] args）{
MyType aMember;
...
aMember = new MyType（...）
...
}
然而，在C ++中，这似乎不起作用。我在课堂上宣布（这是串口通信的
），如下所示：
#include< fstream>
#include< boost / thread / thread.hpp>
class COMConn {
public：
COMConn（int port ）;
~COMConn（）;
char * send（char）;
char * send（char，char [ ]）;
私人：
void connect（int）;
std :: ifstream输入;
std :: ofstream输出;
boost :: thread inputthread;
boost :: thread outputthread;
} ;
但是当我想初始化线程和流时，我想做
类似
void COMConn :: connect（int port）{
this-> input = std :: ifstream（" COM1："）;
this-> inputthread = boost :: thread（& input.read）; //不正确，需要
参数，但暂时跳过这个
//等等其他人
}
如何在C ++中执行此操作？我发现我可以做
this-> input.open（" COM1："）;
但这不是一般的工作原理。我发现这个
非常混乱我必须说...谢谢你的任何建议
Coming from writing mostly in Java, I have trouble understanding how to
declare a member without initializing it, and do that later... In Java,
I would write something like
public static void main(String[] args) {
MyType aMember;
...
aMember = new MyType(...)
...
}
However, in C++ this does not seem to work. I declare in class (it''s
for serial port communication) like this:
#include <fstream>
#include <boost/thread/thread.hpp>
class COMConn {
public:
COMConn(int port);
~COMConn();
char *send(char);
char *send(char, char[]);
private:
void connect(int);
std::ifstream input;
std::ofstream output;
boost::thread inputthread;
boost::thread outputthread;
};
But when I want to initialize the threads and streams, I want to do
something like
void COMConn::connect(int port) {
this->input = std::ifstream("COM1:");
this->inputthread = boost::thread(&input.read); // Not correct, needs
arguments, but skip that for now
//etc for the others
}
How do you go about doing this in C++? I found that I could do
this->input.open("COM1:");
But that is hardly something that will work in general. I find this
very confusing I must say... Thanks you for any advice
推荐答案
<
Calle Pettersson写道：
Calle Pettersson wrote:
来自写作主要是用Java编写，我无法理解如何使用
声明一个成员没有初始化，并在以后这样做...
Coming from writing mostly in Java, I have trouble understanding how to
declare a member without initializing it, and do that later...
一般规则：不要。只需将声明移动到你初始化它的位置，因为任何对象在初始化之前都是不可用的。
你不必先声明变量;这是一个古老的C习惯
不是
甚至在今天的C语言中都需要，更不用说新语言了。
HTH
Michiel Salters
General rule: don''t. Just move the declaration to the point where you
initialize it, as any object is unusable until initialized.
You don''t have to declare variables first; that''s a old C habit which
is not
even needed in today''s C, let alone in newer languages.
HTH
Michiel Salters
Mi ************* @ tomtom.com 写道：
Calle Pettersson写道：
Calle Pettersson wrote:
来自写作主要是用Java编写，我无法理解如何在没有初始化的情况下声明成员
它，以后再做...
Coming from writing mostly in Java, I have trouble understanding how to
declare a member without initializing it, and do that later...
一般规则：不要。只需将声明移动到你初始化它的位置，因为任何对象在初始化之前都是不可用的。
你不必先声明变量;这是一个古老的C习惯
不是
甚至在今天的C语言中都需要，更不用说新语言了。
HTH
Michiel Salters
General rule: don''t. Just move the declaration to the point where you
initialize it, as any object is unusable until initialized.
You don''t have to declare variables first; that''s a old C habit which
is not
even needed in today''s C, let alone in newer languages.
HTH
Michiel Salters
真的吗？但是如果我需要这个可以访问类，但是不能
在类定义中调用构造函数？ （在这种情况下需要知道哪个com
端口）
另外，我不知道如果变量可以添加到类中，如果它们是
$标题中没有指定b $ b吗？
或者我误解了你？
Really? But if I need this to be accessible to the class, but can''t
call the constructor in the class definition? (Need to know which com
port in this case)
Also, I didn''t know that variables could be added to a class if they
aren''t specified in the header?
Or am I misunderstanding you?
Calle Pettersson写道：
Calle Pettersson wrote:
Mi *********** **@tomtom.com 写道：
> Calle Pettersson写道：
>Calle Pettersson wrote:
>>来自写作主要是用Java编写的，我无法理解
如何在不初始化的情况下声明成员，并且稍后执行此操作
稍后...
>>Coming from writing mostly in Java, I have trouble understanding
how to declare a member without initializing it, and do that
later...
一般规则：不要。只需将声明移动到初始化它的位置，因为任何对象在初始化之前都是不可用的。
您不必先声明变量;这是一种古老的C习惯，在今天的C语言中甚至不需要，更不用说新语言了。
HTH
Michiel Salters
General rule: don''t. Just move the declaration to the point where you
initialize it, as any object is unusable until initialized.
You don''t have to declare variables first; that''s a old C habit which
is not
even needed in today''s C, let alone in newer languages.
HTH
Michiel Salters
真的吗？但是如果我需要这个可以访问类，但是不能
在类定义中调用构造函数？ （在这种情况下需要知道哪个com
端口）
另外，我不知道如果变量可以添加到类中，如果它们是
$标题中没有指定b $ b吗？
或者我误解了你？
Really? But if I need this to be accessible to the class, but can''t
call the constructor in the class definition? (Need to know which com
port in this case)
Also, I didn''t know that variables could be added to a class if they
aren''t specified in the header?
Or am I misunderstanding you?
看来你们彼此误解了。
*会员*在类定义中首先被声明。然后，在构造函数的
初始化列表中，初始化它们。 *变量*
（非会员，独立）不需要申报。声明/定义/
在需要时初始化它们。
class Class {
void * member; //成员：声明
public：
Class（）：member（0）{} //初始化
};
int main（）{
void * nonmember（0）; //变量：declaration / definition / init''n
}
V
-
请在通过电子邮件回复时删除资本''A'
我没有回复最热门的回复，请不要问
It seems you''re misunderstanding each other.
*Members* are declared first, in the class definition. Then, in the
initialiser list of a constructor, they are initialised. *Variables*
(non-member, stand-alone) don''t need to be declared. Declare/define/
initialise them when needed.
class Class {
void *member; // a member: declaration
public:
Class() : member(0) {} // initialisation
};
int main() {
void *nonmember(0); // a variable: declaration/definition/init''n
}
V
--
Please remove capital ''A''s when replying by e-mail
I do not respond to top-posted replies, please don''t ask
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