对end的引用模棱两可[重复]

Question

谁能解释为什么我在代码后面得到“对'end'的引用是模棱两可的”？我明白这是因为与STD：：END发生冲突。但是如果我把结束放在主函数中，它不会显示错误。在全局范围内定义与在主函数范围内定义有何不同？

#include<bits/stdc++.h>

using namespace std;
int *end;

int main() {
    return end == NULL;
}

prog.cpp: In function 'int main()':
prog.cpp:7:12: error: reference to 'end' is ambiguous
     return end == NULL;
            ^
prog.cpp:4:6: note: candidates are: int* end
 int *end;
      ^
In file included from /usr/include/x86_64-linux-gnu/c++/5/bits/stdc++.h:94:0,
                 from prog.cpp:1:
/usr/include/c++/5/valarray:1226:5: note:                 template<class _Tp> const _Tp* std::end(const std::valarray<_Tp>&)
     end(const valarray<_Tp>& __va)
     ^
/usr/include/c++/5/valarray:1216:5: note:                 template<class _Tp> _Tp* std::end(std::valarray<_Tp>&)
     end(valarray<_Tp>& __va)
     ^
In file included from /usr/include/c++/5/string:51:0,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/istream:38,
                 from /usr/include/c++/5/sstream:38,
                 from /usr/include/c++/5/complex:45,
                 from /usr/include/c++/5/ccomplex:38,
                 from /usr/include/x86_64-linux-gnu/c++/5/bits/stdc++.h:52,
                 from prog.cpp:1:
/usr/include/c++/5/bits/range_access.h:97:5: note:                 template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::end(_Tp (&)[_Nm])
     end(_Tp (&__arr)[_Nm])
     ^
/usr/include/c++/5/bits/range_access.h:78:5: note:                 template<class _Container> decltype (__cont.end()) std::end(const _Container&)
     end(const _Container& __cont) -> decltype(__cont.end())
     ^
/usr/include/c++/5/bits/range_access.h:68:5: note:                 template<class _Container> decltype (__cont.end()) std::end(_Container&)
     end(_Container& __cont) -> decltype(__cont.end())
     ^
In file included from /usr/include/c++/5/bits/range_access.h:36:0,
                 from /usr/include/c++/5/string:51,
                 from /usr/include/c++/5/bits/locale_classes.h:40,
                 from /usr/include/c++/5/bits/ios_base.h:41,
                 from /usr/include/c++/5/ios:42,
                 from /usr/include/c++/5/istream:38,
                 from /usr/include/c++/5/sstream:38,
                 from /usr/include/c++/5/complex:45,
                 from /usr/include/c++/5/ccomplex:38,
                 from /usr/include/x86_64-linux-gnu/c++/5/bits/stdc++.h:52,
                 from prog.cpp:1:
/usr/include/c++/5/initializer_list:99:5: note:                 template<class _Tp> constexpr const _Tp* std::end(std::initializer_list<_Tp>)
     end(initializer_list<_Tp> __ils) noexcept
     ^

Answer 1

在使用using namespace std；将整个std命名空间引入当前（全局）作用域后，编译器无法区分（globals)int*end和std：：end。避免使用使用名称空间std；。