Is this function overloading correct? - c++

Question

Consider having these four functions in one C++ program:
void a(int val)
{
cout<<val;
}
void a(int &val)
{
cout<<val;
}
void a(int *val)
{
cout<<val;
}
void a(double val)
{
cout<<val;
}
Few Questions i have are:
Is there going to be any error in the code? or are they all overloaded without any error.
Can you tell me how to call all of these four functions correctly? My try was below:
int iTmp;
int *pTmp;
double dTmp;
a(iTmp);
a(iTmp);
a(pTmp);
a(dTmp);

Answer 1

The only problem are the functions:
void a(int &val)
and
void a(int val)
The compiler will create the following errors:
Compilation error time: 0 memory: 3140 signal:0
prog.cpp: In function 'int main()':
prog.cpp:28:8: error: call of overloaded 'a(int&)' is ambiguous
a(iTmp);
^
Because he cant distinguish both, if you remove one of them the compilation succeeds
See Example:
#include <iostream>
using namespace std;
void a(int val)
{
cout<<val;
}
void a(int *val)
{
cout<<val;
}
void a(double val)
{
cout<<val;
}
int main() {
int iTmp = 0;
int *pTmp = 0;
double dTmp = 0.0;
a(iTmp);
a(iTmp);
a(pTmp);
a(dTmp);
return 0;
}
See working example:
http://ideone.com/WRZUoW

Answer 2

Your code will compile but calling
int iTmp;
a(iTmp);
will yield an ambiguous overload resolution call since both
void a(int val)
{
cout<<val;
}
void a(int &val)
{
cout<<val;
}
will match.
The reason for this lies in the standard:
[over.match.best]
A viable function F1 is defined to be a better function than another viable function F2 if for all arguments i, ICSi(F1) is not a worse conversion sequence than ICSi(F2)
int->int
int->int&
these are standard conversion sequences and the entire list of [over.ics.rank]p3.2 is checked without success for a better conversion sequence (exact match in both cases)
They are thus deemed "undistinguishable".
A word of advice: the variable are also not initialized and (if automatic variables) even if your code compiled, the output would be undefined.

Answer 3

The compiler must be able to know what function to call.
With
int i = 12;
a(i);
both a(int i) and c(int& i) are acceptable candidates and compiler throws an error.
and
void a(const int& i) { ... }
will suffer from same problem.

Answer 4

These two function will cause issues
void a(int val)
{
cout<<val;
}
void a(int &val)
{
cout<<val;
}
Your call a(iTmp); have two possible candidates. Compiler should shown an error for these. Otherwise pointer argument(int *val)and double argument(double val) are okay.

Answer 5

The most obvious problem is that
void a(int val) {
and
void a(int& val) {
are ambiguous when called with iTmp.
Aside from that, depending on whether the variables are global or local ones, the code is using uninitialized variables -> UB and whether or not,
void a(int* val) {
std::cout << val << std::endl;
}
is overloaded correctly is up for debate. I'd assume that it should be std::cout << *val << std::endl;, but that of course depends on what the function is supposed to do (although a function that prints an address would usually be parameterized by (void* or char*);