CODEWITHSUNDEEP
c++
Jabberwocky
Jabberwocky

Reputation: 50775

Function overloading and confusion between double and long

I expected this simple code to compile:

void Foo(long a, long);
void Foo(long a, double b);

int main()
{
  Foo(1, 2);
  Foo(1, 2.0);
}

Compiler output:

prog.cpp: In function ‘int main()’:
prog.cpp:8:11: error: call of overloaded ‘Foo(int, int)’ is ambiguous
   Foo(1, 2);
           ^
prog.cpp:3:6: note: candidate: void Foo(long int, long int)
 void Foo(long a, long);
      ^~~
prog.cpp:4:6: note: candidate: void Foo(long int, double)
 void Foo(long a, double b);
      ^~~

I don't understand why the call is ambigous. For me Foo(unsigned long a, unsigned long) is clearly a closer match than void Foo(unsigned long a, double b) for Foo(1, 2).

But if I replace long by int it compiles:

void Foo(int a, int);
void Foo(int a, double b);

int main()
{
  Foo(1, 2);
  Foo(1, 2.0);
}

I'm really lost here.

Upvotes: 0

Views: 43

Answers (1)

Bathsheba
Bathsheba

Reputation: 234705

1 and 2 are literals of type int, and 2.0 is a double.

So neither overload is an exact match for your types, they are ranked similarly for the purposes of overload resolution, so the compiler is required to issue a diagnostic. (Note that int and long must be different types even if they have the same size and complementing scheme.)

You could fix with Foo(1L, 2L);.

Upvotes: 5

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