When default parameters are not specified, function overloading works.
But, why doesn’t function overloading work when default parameters are specified?
This program takes two integers and compares them to find the larger of the two.
Then, it compares the maximum value with bigger integers obtained earlier, and the smaller value is output.
Here’s the code I written
#include <iostream>
using namespace std;
int big(int a, int b);
int big(int a, int b, int max = 100);
int big(int a, int b) {
if (a > b)
if (a > 100)
{
return 100;
}
else {
return a;
}
else {
if (b > 100) {
return 100;
}
else
{
return b;
}
}
}
int big(int a, int b, int max) {
if (a > b) {
if (a < max) {
return a;
}
else
{
return max;
}
}
else {
if (b < max) {
return b;
}
else {
return max;
}
}
}
int main() {
int x = big(3, 5);
int y = big(300, 60);
int z = big(30, 60, 50);
cout << x << ' ' << y << ' ' << z << endl;
return 0;
}
When I debug the code I wrote, it says
E0308
Compilation Error: More than one instance of overloaded function matches the argument list
I learned that function overloading can work when the function parameters are different.
In my code, function names are the same, but function parameters are different:
(int x, int y) and (int x, int y, int max)
But it doesn’t work.
In conclusion, why does function overloading not work when default parameters are specified?
IDE that I used:
Microsoft Visual Studio Community 2022 (64-bit) – Current
version. 17.5.1
Here’s the desire result:
- Variables
x
andy
have the return value of the first functionbig(int x, int y)
- Variable
z
has the return value of the second functionbig(int x, int y, int max = 100)
This Question is related, but I don’t understand how the solution is what I want.
2
Answers
You’ve effectively got these two functions named the same
And then when you invoke
big(3,5)
….Exactly which version of
big
did you expect to get called? The first implementation which explicitly takes two parameters or the second implementation that can take two or three parameters?The compiler is doing you a favor by erroring out and telling you it’s ambiguous.
As I called out in my comments, function overloading is overrated. Just name the functions explicitly such that there is zero ambiguity on which implementation is getting called.
Also, your entire implementation can be simplified to just a single function and two lines of code
The default parameter for max seems innocuously ok to me if you keep it as a single function with no overloads.
This part is ambiguous, since the second function declaration has a default argument:
So while you call, for example, big(20,30), both versions of big() could be used. So there will be 2 candidates.
It would be enough to use the second version of your function to make it work without overloading.
Something like this :
In case you still want to define 2 functions. I would suggest you remove the default argument.
Extra note: About declare and define your functions. Since you define the function int the same source file and before main(), perhaps you do not need to declare and then define. So you could skip to declare it. If you move the implementation to another source file or after main(), then declare it.
More info: Link