Using default values in C++ Function declaration [duplicate]

Question

It's been quite a while (18+ years) since I've been coding in C++.

I am running into a problem with using default parameters in a function, then trying to call that function with only the non defaulted parameter. As an example here is my class declaration

//foo.h
#pragma once
struct foo
{
  void bar(int, int, int);
  void snafu();
}

I then try to call foo::bar(3) from within the foo::snafu() function.

//foo.cpp
#include "foo.h"
void foo::bar(int x, int y = 1, int z =2)
{
... do stuff
}

void foo::snafu()
{
  foo::bar(5) //Error C22660 Function does not take 1 argument
}

Side note : If it has been that long since you used C++, read this C++ core guidelines a lot has changed since then so it might be good for you to pickup a bit of the latest idioms :) As for your problem that's mostly a typo, the default parameters are in the wrong place — Pepijn Kramer
– Pepijn Kramer, Commented Oct 18, 2024 at 20:16
remove the defaults from the definition, they should only be in the declaration, otherwise the compiler will fail to compile the definition and you will get an unresolved symbol error — Ahmed AEK
– Ahmed AEK, Commented Oct 18, 2024 at 20:19
The syntax errors in your code indicate that it was not copy-pasted. When I fixed them, your code compiled. Details matter. Copy-paste code; don't try to type it in the question. — JaMiT
– JaMiT, Commented Oct 18, 2024 at 20:23

Remy Lebeau · Accepted Answer · 2024-10-18 20:19:54Z

2

You need to put the default values in the declaration of the method, not in the definition.

foo.h

#pragma once

struct foo
{
  void bar(int x, int y = 1, int z = 2);
  ...
}

foo.cpp

#include "foo.h"

void foo::bar(int x, int y, int z)
{
    ... do stuff
}

...

Also, you have 2 typos in your foo:snafu() definition. You are using : instead of ::, and you don't need to refer to bar() as foo::bar() inside of snafu().

void foo::snafu()
{
    bar(5);
}

answered Oct 18, 2024 at 20:19

Remy Lebeau

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1 Comment

Jesse Knott Over a year ago

Thanks! Also thanks for catching the typos, I'll update the code to keep it right for future views

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