std :: map< int，std :: string [2]>问题 [英] std::map<int, std::string[2]> problems
问题描述
首先，请原谅我，如果这是一个错误的地方提出这个问题，
如果这是一个愚蠢的问题（这是我用C ++的第二周），或者如果这个是
回答了其他地方（我已搜索但未找到任何东西）。
这里有问题，我有两套文件，文件的名称包含一个
数字，对于每个集合都是唯一的，但是可能（甚至可能）
不同集合中的两个文件具有相同的数字。我希望以这样的方式存储这些
文件名，以便我可以通过它们的编号来检索它们。对于这个
我以为我会使用一个数字作为键的地图，一个字符串数组
来存储文件名，但是我已经尝试使用
此解决方案时遇到麻烦。
将文件名添加到地图时我不知道文件名是否来自
其他套装已经存在，但举例说明：
http://www.fredosaurus.com/notes-cpp.../map/pair.html
http://www.fredosaurus.com/notes-cpp。 ..- wordfreq.html
它创建了未找到的条目，如果找到它们我可以
修改它们。
这里的代码显示我的问题：
#include< map>
#include< string>
#include< vector>
使用std :: map;
使用std :: string;
使用std :: vector;
class Files
{
public：
void nextFile（string *，string *）;
void open（vector< string> *，int）;
private：
int getNumber（string）; //从文件名中获取数字
map< int，string [2]> fileSets;
map< int，string [2]> :: iterator iter;
};
//返回下一对文件
//我已经删除了一些代码以保持简短，
//除其他外检查fileSets.end（）。
void Files :: nextFile（string * file1，string * file2）
{
iter ++;
/ /返回指向文件名的指针
file1 =&（iter-> second [0]）;
file2 =&（iter-> second [1 ]）;
}
//将文件添加到集合
//文件是一个带有要添加的文件名的向量。 />
// setNr是文件应该添加的集合的数量，可以是0或1.
void Files :: open（vector< string> * files，int setNr）
{
if（setNr< 2）
{
for（int i = 0; i< files-> size（）; i ++）
{
//将文件添加到正确的集合
int fileNumber = getNumber（（* files）[i]）;
（fileSets [fileNumber]）[setNr] =（* files）[i];
//这不起作用^^^^^^^
}
}
//设置迭代器
iter = fileSets.begin（）;
}
----------------------------------- -------
在gcc 3.3上编译时，我得到以下内容：
/usr/include/c++/3.3。 4 / bits / stl_map.h：在成员函数`_Tp& std :: map< _Key，
_Tp，_Compare，_Alloc> :: operator []（const _Key&）[with _Key = int，_Tp =
std :: string [2]，_ Compare = std :: less< int>，_ Alloc =
std :: allocator< std :: pair< const int，std :: string [2]> >]''：
Files.cpp：46：从这里实例化
/usr/include/c++/3.3.4/bits/stl_map.h:319：错误：ISO C ++禁止转换为
数组类型`std :: string [2]''
---------- --------------------------------
我在使用gcc 3.4时得到了类似的结果。很显然，阵列存在一些问题
，但是我无法弄清楚是什么，并且会欣赏
正确的方向，并且因为我'''我还在学习任何其他评论。
PS：
如果密钥未知，则无法随机访问地图
但如果我有一个（双向）迭代器指向
映射中的某个元素，并且知道我感兴趣的元素是来自一个元素的N个元素br />
迭代器当前指向我可以通过向迭代器添加
N来跳转到该元素，例如iter + = N？
-
Erik Wikstr？m
First of all, forgive me if this is the wrong place to ask this question,
if it''s a stupid question (it''s my second week with C++), or if this is
answered some place else (I''ve searched but not found anything).
Here''s the problem, I have two sets of files, the name of a file contains a
number which is unique for each set but it''s possible (even probable) that
two files in different sets have the same numbers. I want to store these
file-names in such a way that I can retrieve them by their number. For this
I thought I''d use a map with the number as the key an an array of strings
to store the file-names, however I''ve run into trouble when trying to use
this solution.
When adding the file-names to the map I don''t know if a filename from the
other set already exists, but given examples at:
http://www.fredosaurus.com/notes-cpp.../map/pair.html
http://www.fredosaurus.com/notes-cpp...-wordfreq.html
it seams like entries not found are created and if they are found I can
modify them.
Here''s code that displays my problem:
#include <map>
#include <string>
#include <vector>
using std::map;
using std::string;
using std::vector;
class Files
{
public:
void nextFile(string*, string*);
void open(vector<string>*, int);
private:
int getNumber(string); // Gets the number from the filename
map<int, string[2]> fileSets;
map<int, string[2]>::iterator iter;
};
// Return the next pair of files
// I''ve removed a bit of code to keep it short,
// among other things checks for fileSets.end().
void Files::nextFile(string* file1, string* file2)
{
iter++;
// Return the pointers to the filenames
file1 = &(iter->second[0]);
file2 = &(iter->second[1]);
}
// Add files to the sets
// files is a vector with the filenames to be added.
// setNr is the number of the set the files should be
// added to, can be 0 or 1.
void Files::open(vector<string>* files, int setNr)
{
if(setNr < 2)
{
for(int i = 0; i < files->size(); i++)
{
// Add the file to the correct set
int fileNumber = getNumber((*files)[i]);
(fileSets[fileNumber])[setNr] = (*files)[i];
// This does not work ^^^^^^^
}
}
// Set the iterator
iter = fileSets.begin();
}
------------------------------------------
When compiling on gcc 3.3 I get the following:
/usr/include/c++/3.3.4/bits/stl_map.h: In member function `_Tp& std::map<_Key,
_Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = int, _Tp =
std::string[2], _Compare = std::less<int>, _Alloc =
std::allocator<std::pair<const int, std::string[2]> >]'':
Files.cpp:46: instantiated from here
/usr/include/c++/3.3.4/bits/stl_map.h:319: error: ISO C++ forbids casting to an
array type `std::string[2]''
------------------------------------------
and I get similar results when using gcc 3.4. Obviously there''s some problem
with the array but I can''t figure out what and would appreciate a nudge in the
right direction, and since I''m still learning any other comment too.
PS:
It''s not possible to get random access to a map if the key is not known
but if I have an (bidirectional) iterator pointing at some element in the
map, and know that the element I''m interested in is N elements from the one
the iterator is currently pointing at can I jump to that element by adding
N to the iterator, e.g. iter+=N ?
--
Erik Wikstr?m
推荐答案
Erik Wikstr？m写道：
Erik Wikstr?m wrote:
首先，请原谅我这个问题是错误的，
不是。你很好。
如果这是一个愚蠢的问题（这是我用C ++的第二周），或者如果这是在其他地方回答的话（我已经搜索但没有找到任何东西）。
它可能已经被回答了，但有时它很难找到。
[...]
map< int，string [2]>文件集;
你根本做不到。数组不能是标准
容器中的存储数据。如果你需要两个字符串，要么成对（std :: pair）
或制作你自己的结构。
[...]
First of all, forgive me if this is the wrong place to ask this question,
It''s not. You''re fine.
if it''s a stupid question (it''s my second week with C++), or if this is
answered some place else (I''ve searched but not found anything).
It may have been answered already, but sometimes it''s rather hard to find.
[...]
map<int, string[2]> fileSets;
You simply can''t do that. Arrays cannot be the stored data in a standard
container. If you need two strings there, either make a pair (std::pair)
or make your own struct.
[...]
V
V
" Erik Wikstr？m" < ER *********** @ telia.com> schrieb im Newsbeitrag
新闻：XO ******************* @ newsb.telia.net ...
"Erik Wikstr?m" <er***********@telia.com> schrieb im Newsbeitrag
news:XO*******************@newsb.telia.net...
这就是问题所在，我有两组文件，一个文件的名称包含
一个数字，这个数字对于每一组都是唯一的，但它可能（甚至可能）
不同组中的两个文件具有相同的数字。我希望以这样的方式存储这些文件名，以便我可以通过它们的编号来检索它们。对于
这个
我以为我会用一个数字作为键的地图，一个字符串数组来存储文件名，但是我遇到了麻烦。试图使用这个解决方案。
正如Victor已经解释过的那样，你不能使用C风格的数组作为标准容器的值
类型。但是你可以使用std :: vector。
但是，当你描述你的问题时，你有两组文件，而不是一组
文件对。所以我建议使用两个
std :: map< int，std :: string>的实例，每组文件一个。
PS：
如果密钥未知，则无法随机访问地图
但如果我有一个（双向）迭代器指向
地图中的某个元素，并且知道该元素我感兴趣的是来自
的N个元素。迭代器当前指向的是我可以通过向迭代器添加
N来跳转到该元素，例如iter + = N？
Here''s the problem, I have two sets of files, the name of a file contains
a
number which is unique for each set but it''s possible (even probable) that
two files in different sets have the same numbers. I want to store these
file-names in such a way that I can retrieve them by their number. For
this
I thought I''d use a map with the number as the key an an array of strings
to store the file-names, however I''ve run into trouble when trying to use
this solution.
As Victor already explained, you cannot use a C style array as the value
type of a standard container. But you could use an std:: vector instead.
However, as you describe your problem, you have two sets of files, not one
set of pairs of files. So I would suggest to use two instances of
std::map<int, std::string>, one for each set of files.
PS:
It''s not possible to get random access to a map if the key is not known
but if I have an (bidirectional) iterator pointing at some element in the
map, and know that the element I''m interested in is N elements from the
one
the iterator is currently pointing at can I jump to that element by adding
N to the iterator, e.g. iter+=N ?
看看std :: advance。
HTH
Heinz
Have a look at std::advance.
HTH
Heinz
> map< int，string [2]> fileSets;
string [2]没有=运算符且没有<运营商 - 这就是整个
问题。
-Gernot
> map<int, string[2]> fileSets;
string[2] has no = operator and no < operator - that''s the whole
problem.
-Gernot
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