[英]unordered_map iterator printing using cout
I'm trying to use an iterator to output an integer in a multilayered unordered_map and I'm having trouble with it, the error is below the code. 我正在尝试使用迭代器在多层unordered_map中输出整数,但我遇到了麻烦,该错误在代码下方。
#include <boost/unordered_map.hpp>
#include <iostream>
using namespace std;
int main()
{
typedef boost::unordered_map <int, boost::unordered_map<int, int> > _map;
_map MAP;
boost::unordered_map<int, int>::iterator map_it;
MAP[0][0] = 10;
map_it = MAP[0].begin();
cout<<*map_it<<endl;
return 0;
}
error below: 错误如下:
unordered_map_iterator\unordered_map_iterator.cpp||In function 'int main()':|
unordered_map_iterator\unordered_map_iterator.cpp|16|error: no match for 'operator<<' in 'std::cout << map_it.boost::unordered_detail::hash_iterator<A, G>::operator* [with A = std::allocator<std::pair<const int, int> >, G = boost::unordered_detail::ungrouped]()'|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|108|note: candidates are: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>& (*)(std::basic_ostream<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|117|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ios<_CharT, _Traits>& (*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|127|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|165|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|169|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|173|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\bits\ostream.tcc|91|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|180|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\bits\ostream.tcc|105|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|191|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|200|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|204|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|209|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|213|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|221|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\ostream|225|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\bits\ostream.tcc|119|note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_streambuf<_CharT, _Traits>*) [with _CharT = char, _Traits = std::char_traits<char>]|
||=== Build finished: 1 errors, 0 warnings ===|
To be able to do this: 为了能够做到这一点:
cout<<*map_it<<endl;
You will have to overload a <<
operator to support your class _map
. 您将必须重载<<
操作符以支持您的_map
类。
<<
is designed to work with standard data types and not custom data type like your class. <<
设计用于标准数据类型,而不是像您的类那样的自定义数据类型。
<<
does not understand the custom class type _map
and hence the error. <<
不了解自定义类类型_map
,因此不正确。
So to do it with the statement you mention, you will have to overload <<
to accept _map
as an parameter. 因此,要使用您提到的语句来完成此操作,就必须重载<<
以接受_map
作为参数。
Alternatively, You can call <<
with arguments it can understand and the ones it is implemented for, 另外,您可以调用<<
带有其可以理解的参数以及为其实现的参数,
cout<<map_it->second<<endl;
This ensures that the argument being passed to <<
is a data type it understands and hence it will work. 这样可以确保传递给<<
的参数是它可以理解的数据类型,因此它将起作用。
boost::unordered_map
's iterator is a std::pair. boost::unordered_map
的迭代器是std :: pair。 Since you have two levels you have to get the proper iterator to each level like this: 由于您有两个级别,因此必须像这样将适当的迭代器添加到每个级别:
typedef boost::unordered_map <int, boost::unordered_map<int, int> > _map;
_map MAP;
MAP[0][0] = 10;
_map::iterator map_it = MAP.begin();
// map_it is an iterator, where first is the key (0), and
// second is the value (boost::unordered_map<int, int>)
boost::unordered_map<int, int>::iterator internal_map_it = map_it->second.begin();
// internal_map_it is an iterator, where first is the key (also 0)
// and second is the value (10)
cout<< internal_map_it->second <<endl;
boost::unordered_map::iterator
points to a pair of values, the first of which is the key, and the second the value. boost::unordered_map::iterator
指向一对值,第一个是键,第二个是值。 So, this line 所以这条线
cout << *map_it << endl;
is trying to print an std::pair
. 正在尝试打印std::pair
。
If you want to print the contents of MAP[0][0]
use 如果要打印MAP[0][0]
的内容,请使用
cout << map_it->second << endl;
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