C ++
当我尝试在gcc 4.7下使用std::distance与自定义迭代器时，它抱怨找不到difference_type 。 我很遗憾不知道为什么它失败了。
#include <iterator>
class nit {
public:
typedef int difference_type;
};
int main() {
const nit test1;
std::distance( test1, test1 );
return 0;
}
给出错误：
/usr/include/c++/4.7/bits/stl_iterator_base_funcs.h:114:5: error: no type named 'difference_type' in 'struct std::iterator_traits<nit>'
你有没有试过定义所有需要的类型/操作符？
#include <iterator>
struct nit
{
typedef std::random_access_iterator_tag iterator_category;
typedef int value_type;
typedef int difference_type;
typedef int* pointer;
typedef int& reference;
bool operator==(nit const&)
{
return true;
}
bool operator!=(nit const&)
{
return false;
}
int operator-(nit const&)
{
return 0;
}
nit()
{
}
};
int main()
{
nit const test1;
std::distance(test1, test1);
return 0;
}
无论如何，你必须在你的类中提供所有类型定义（有或没有std :: iterator的帮助），std :: iterator_traits正在期待或者你必须自己专门化std :: iterator_traits。
此版本的GCC发出其他错误消息，但不会改变您的代码非法的事实。
prog.cpp: In function ‘int main()’:
prog.cpp:9: error: uninitialized const ‘test1’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++v4/bits/stl_iterator_base_types.h: At global scope:
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h: In instantiation of ‘std::iterator_traits<nit>’:
prog.cpp:10: instantiated from here
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h:133: error: no type named ‘iterator_category’ in ‘class nit’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h:134: error: no type named ‘value_type’ in ‘class nit’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h:136: error: no type named ‘pointer’ in ‘class nit’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_types.h:137: error: no type named ‘reference’ in ‘class nit’
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_funcs.h: In function ‘typename std::iterator_traits<_Iterator>::difference_type std::distance(_InputIterator, _InputIterator) [with _InputIterator = nit]’:
prog.cpp:10: instantiated from here
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_iterator_base_funcs.h:119: error: no matching function for call to ‘__iterator_category(nit&)’
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