null或nil或初始化的std :: list iterator？ [英] null or nil or initialised std::list iterator?

问题描述

我想知道如何设置std :: list迭代器变量使其成为

null或nil。如果这不可能，那么

未初始化的std :: list迭代器的值是否可以将此值赋给

std :: list迭代器变量（或者更好的是使用单独的bool

变量作为空标志？）


例如

struct mystru

{

std :: string nm;

int qty;

}

std :: list< mystru> :: iterator i;


//我的价值是多少？

....

i = somelist.begin（）;

//用我做的事情

....

i = NULL_VALUE？

解决方案

sa ************ @ hotmail.com 写道：

我想知道如何设置std :: list iterator变量使它成为null或nil。如果这不可能，那么
未初始化的std :: list迭代器的值是否可以将此值赋给
std :: list iterator变量（或者更好地使用单独的bool
变量为null flag？）

struct mystru
{
std :: string nm;
int数量;
}

std :: list< mystru> :: iterator i;

//我的价值是多少？


未指定。你不能使用我而不给它一个值

...
我= somelist.begin（）;
//用我做的事情
。 ..
i = NULL_VALUE？

i = somelist.end（）; //容器的结束迭代器是一个过了容器的

结尾

Alipha写道：

未指定。 $不能给它一个价值


我认为这就是重点，我想知道它什么时候没有价值

有一个值还是算数呢？


iterator怎么样（NULL）？

sa************@hotmail.com 写道：

未指定。你不能使用我而不给它一个价值

我认为这就是重点，我想知道什么时候它没有价值或者算不上使用它呢？

iterator（NULL）怎么样？

使用指向迭代器的指针，将其设置为0表示缺席。

迭代器没有空状态。


Marc

I want to know how to set an std::list iterator variable to make it
null or nil. If this is not possible what is the value of an
uninitialised std::list iterator and is it ok to assign this value to a
std::list iterator variable (or is it better to use a seperate bool
variable as a "null flag" ?)

e.g.
struct mystru
{
std::string nm;
int qty;
}

std::list<mystru>::iterator i;

// what is the value of i ?
....
i = somelist.begin();
// do things with i
....
i = NULL_VALUE?

解决方案

sa************@hotmail.com wrote:

I want to know how to set an std::list iterator variable to make it
null or nil. If this is not possible what is the value of an
uninitialised std::list iterator and is it ok to assign this value to a
std::list iterator variable (or is it better to use a seperate bool
variable as a "null flag" ?)

e.g.
struct mystru
{
std::string nm;
int qty;
}

std::list<mystru>::iterator i;

// what is the value of i ?
unspecified. you CAN''T use i without giving it a value
...
i = somelist.begin();
// do things with i
...
i = NULL_VALUE?

i = somelist.end(); // the end iterator of a container is one-past the
end of the container

Alipha wrote:

unspecified. you CAN''T use i without giving it a value

I think that is the point, I want to know when it does not
have a value or does that count as using it too?

what about iterator(NULL) ?

sa************@hotmail.com wrote:

unspecified. you CAN''T use i without giving it a value

I think that is the point, I want to know when it does
not have a value or does that count as using it too?

what about iterator(NULL) ?

Use a pointer to iterator, set it to 0 to signal absence.
iterators don''t have a Null State.

Marc

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