使用较少的< string> ... [英] using less<string>...

问题描述

- - - - - - - - - - - - - - -

#include< iostream>

#include< string>

#include< map>

using namespace std;


int main （）

{

字符串名称;

int pop;


string states [] = {" Wyoming"，" Colorado"，" Nevada"，

" Montana"，" Arizona"，" Idaho"};

int pops [] = {470,2890,800,787,2718,944};

map< string，int，less< string> > mapStates;


//尝试用以下内容替换上面的内容：

// map< string，int> mapStates;

map< string，int，less< string> > :: iterator iter; // iterator


for（int j = 0; j< 6; j ++）

{

name = states [j ]。 //从数组中获取数据

pop = pops [j];

mapStates [name] = pop; //把它放在地图

}

cout<< 输入状态：; //从用户获取状态


cin>>姓名;

pop = mapStates [name]; //找到人口

cout<< 人口： << pop<< "，000; \\ n";


cout<< ENDL; //显示整个地图

for（iter = mapStates.begin（）; iter！= mapStates.end（）; iter ++）

cout<< （* iter）.first<< ''''<< （* iter）.second<< "，000 $ \\ nn ;;

返回0;

}


- - - - - - - - - - - - - - -


问题是：我看不出以下任何区别：

map< string，int，less< string> > mapStates;


和


map< string，int> mapStates;


我试图谷歌一下，发现两行都调用了地图

构造函数来创建一个地图< string，int>和较少的< string>是一个

比较函数 - 一个'弱排序''。我能看到少于< string>

在某处定义了吗？


为什么我看不出这两种方法有什么区别？是少于< string>

默认？是否还有一个< string> -function？

所以我也尝试在 www.cppreference.com 有一些很好的描述，但我找不到它......


有人可以向我澄清这个问题吗？

最好的问候/ Med venlig hilsen

Martin J？rgensen


- -

----------------------------------------- ----------------------------------

Martin J？rgensen的家 - < a rel =nofollowhref =http://www.martinjoergensen.dktarget =_ blank> http://www.martinjoergensen.dk

Hi,

- - - - - - - - - - - - - - -
#include <iostream>
#include <string>
#include <map>
using namespace std;

int main()
{
string name;
int pop;

string states[] = { "Wyoming", "Colorado", "Nevada",
"Montana", "Arizona", "Idaho"};
int pops[] = { 470, 2890, 800, 787, 2718, 944 };
map<string, int, less<string> > mapStates;

// Try replacing the above with:
// map<string, int> mapStates;
map<string, int, less<string> >::iterator iter; //iterator

for(int j=0; j<6; j++)
{
name = states[j]; //get data from arrays
pop = pops[j];
mapStates[name] = pop; //put it in map
}
cout << "Enter state: "; //get state from user

cin >> name;
pop = mapStates[name]; //find population
cout << "Population: " << pop << ",000\n";

cout << endl; //display entire map
for(iter = mapStates.begin(); iter != mapStates.end(); iter++)
cout << (*iter).first << '' '' << (*iter).second << ",000\n";
return 0;
}

- - - - - - - - - - - - - - -

The question is: I don''t see any difference between:
map<string, int, less<string> > mapStates;

and

map<string, int> mapStates;

I tried to google around a bit and found that both lines call the map
constructor to create a map<string, int> and the less<string> is a
comparison function - a ''weak ordering''. Can I see how less<string> is
defined somewhere?

Why don''t I see any difference between both methods? Is less<string>
default? Is there also a more<string>-function?

So I also tried to look for it at www.cppreference.com which has some
nice descriptions but I couldn''t find it...

Can anyone clarify this issue to me?
Best regards / Med venlig hilsen
Martin J?rgensen

--
---------------------------------------------------------------------------
Home of Martin J?rgensen - http://www.martinjoergensen.dk

推荐答案

Martin J？rgensen写道：

Martin J?rgensen wrote:

- - - - - - - - - - - - - - -
#include< iostream>
#include< string>
#include< map>
使用命名空间std;

int main（）
{
字符串名称;
int pop;

string states [] = {" Wyoming"，" Colorado"，" Nevada"，
" Montana"，" Arizona"，" Idaho"};
int pops [] = {470,2890,800,787,2718,944};

map< string，int，less< string> > mapStates;

//尝试用以下内容替换上面的内容：
// map< string，int> mapStates;

map< string，int，less< string> > :: iterator iter; // iterator

for（int j = 0; j< 6; j ++）
{
name = states [j]; //从数组中获取数据
pop = pops [j];
mapStates [name] = pop; //把它放在地图
}
cout<< 输入状态：; //从用户获取状态
cin>> name;
pop = mapStates [name]; //找到人口
cout<< 人口： << pop<< "，000; \\ n";

cout<< ENDL; //显示整个地图
for（iter = mapStates.begin（）; iter！= mapStates.end（）; iter ++）
cout<< （* iter）.first<< ''''<< （* iter）.second<< "，000 \ n";
返回0;
}
- - - - - - - - - - - - - - -

map< string，int，less< string> > mapStates;

和

map< string，int> mapStates;


没有区别。地图的默认比较是

std :: less< Key>所以你只是明确地提供了默认参数。

我试着稍微google一下，发现两行都调用了地图
构造函数来创建一个地图< string，int>和较少的< string>是一个比较函数 - 一个'弱排序''。我能看到少于< string>
是在某个地方定义的吗？

Hi,

- - - - - - - - - - - - - - -
#include <iostream>
#include <string>
#include <map>
using namespace std;

int main()
{
string name;
int pop;

string states[] = { "Wyoming", "Colorado", "Nevada",
"Montana", "Arizona", "Idaho"};
int pops[] = { 470, 2890, 800, 787, 2718, 944 };
map<string, int, less<string> > mapStates;

// Try replacing the above with:
// map<string, int> mapStates;
map<string, int, less<string> >::iterator iter; //iterator

for(int j=0; j<6; j++)
{
name = states[j]; //get data from arrays
pop = pops[j];
mapStates[name] = pop; //put it in map
}
cout << "Enter state: "; //get state from user
cin >> name;
pop = mapStates[name]; //find population
cout << "Population: " << pop << ",000\n";

cout << endl; //display entire map
for(iter = mapStates.begin(); iter != mapStates.end(); iter++)
cout << (*iter).first << '' '' << (*iter).second << ",000\n";
return 0;
}

- - - - - - - - - - - - - - -

The question is: I don''t see any difference between:
map<string, int, less<string> > mapStates;

and

map<string, int> mapStates;
There is no difference. The default Comparison for a map is
std::less<Key> so you''ve simply explicitly provided the default parameter.

I tried to google around a bit and found that both lines call the map
constructor to create a map<string, int> and the less<string> is a
comparison function - a ''weak ordering''. Can I see how less<string> is
defined somewhere?

你可以查看你的实现的定义，尽管最后

你会发现它等同于运算符< ;.


-Mark

You can look at your implementation''s definition although in the end
you''ll find it''s equivalent to operator<.

-Mark

Martin J？rgensen写道：

Martin J?rgensen wrote:

[..]
问题是：我没有看到任何区别：

map< string，int，less< string> > mapStates;

和

map< string，int> mapStates;


没有（除了在前一种情况下输入更多内容）。

我试图谷歌一下，发现两条线都叫地图
构造函数来创建一个地图< string，int>和较少的< string>是一个比较函数 - 一个'弱排序''。我能看到少于< string>是在某处定义的？


它在< functional>中定义标题。

为什么我看不出这两种方法有什么区别？少于< string>
默认？


是。

是否还有更多< string> -function？


不，不是''更多< string>''。它被称为更大< string>。

所以我也试图在 www.cppreference.com 有一些很好的描述，但我找不到它......

任何人都可以向我澄清这个问题吗？

[..]
The question is: I don''t see any difference between:
map<string, int, less<string> > mapStates;

and

map<string, int> mapStates;
There isn''t any (except for more typing in the former case).
I tried to google around a bit and found that both lines call the map
constructor to create a map<string, int> and the less<string> is a
comparison function - a ''weak ordering''. Can I see how less<string> is
defined somewhere?
It''s defined in <functional> header.
Why don''t I see any difference between both methods? Is less<string>
default?
Yes.
Is there also a more<string>-function?
No, not ''more<string>''. It''s called greater<string>.
So I also tried to look for it at www.cppreference.com which has some
nice descriptions but I couldn''t find it...

Can anyone clarify this issue to me?

关于标准库的好书可以。 Nicolai Josuttis发布了一个非常好的
好​​的。


V

-

请删除资金从我通过邮件回复的地址开始

A good book on Standard Library can. Nicolai Josuttis published a very
good one.

V
--
Please remove capital As from my address when replying by mail

Mark P写道：

Martin J？rgensen写道：
-snip-

没有区别。地图的默认比较是
std :: less< Key>所以你只是明确地提供了默认参数。

Martin J?rgensen wrote: -snip-
There is no difference. The default Comparison for a map is
std::less<Key> so you''ve simply explicitly provided the default parameter.

我是这么认为的。

I thought so.

我试着稍微google一下，发现两行都调用地图
构造函数来创建一个地图< string，int>和较少的< string>是一个比较函数 - 一个'弱排序''。我能看到少于< string>
是在某个地方定义的？

I tried to google around a bit and found that both lines call the map
constructor to create a map<string, int> and the less<string> is a
comparison function - a ''weak ordering''. Can I see how less<string> is
defined somewhere?

您可以查看实现的定义，但最终会发现它等同于运算符< ;。

You can look at your implementation''s definition although in the end
you''ll find it''s equivalent to operator<.

我在一台计算机上使用g ++，在另一台计算机上使用MS Visual studio 2005.


我的实现在哪里'定义？

致敬/ Med venlig hilsen

Martin J？rgensen


-

------------------------------------------------ ---------------------------

Martin J？rgensen的故乡 - http://www.martinjoergensen.dk

这篇关于使用较少的&lt; string&gt; ...的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！