why the challenge of the function plus ambiguous

[derk]

#include <functional>
using namespace std;
#define WORD unsigned short
void plus(int len, WORD * a, WORD * b, WORD * c);
int main(){
    WORD M[11],N[11],P[11];
    plus(11,M,N,P);
}
/* Функция вычисляет сумму чисел a и b, результат записывает в c.
 len - длина числа в словах.*/
void plus(int len, WORD * a, WORD * b, WORD * c)
{
 int i,h=0;
 long d;

 for(i=0;i<len;i++)
 {
  //d1=a[i];
  d=(long)a[i]+b[i]+h;
  c[i]=(WORD)d&0xffff;
  h=(d&0x10000l) ? 1 : 0;
 }
}

Please tell me, why is the challenge to function plus is ambigous?

'Cause std:plus accepts two arguments, and here it is defined and transmitted 4

The compiler makes a mistake:

test-ambigous-minus.cpp:7:6: error: reference to 'plus' is ambiguous
    plus(11,M,N,P);
    ^

test-ambigous-minus.cpp:4:10: note: candidate found by name lookup is 'plus'

void plus(int len, WORD * a, WORD * b, WORD * c);

^

/usr/lib/gcc/x86_64-pc-cygwin/4.9.3/include/c++/bits/stl_function.h:167:12: note: candidate found by name lookup is 'std::plus'

struct plus : public binary_function<_Tp, _Tp, _Tp>

^

1 error generated.

[simrah]

Because... std::plus It's not a function, it's a structure.

That's what happened.

namespace std { template<class T> struct plus; }
using namespace std;
void plus(int len, WORD * a, WORD * b, WORD * c);

That's why it's ambiguous.

You don't have to use it. using namespace std;♪