Why does passing an actual array (not an array variable) as an argument to a function throw an error?

Question

So, I was trying to learn pointers from scratch and I hit up on this. I tried doing the following:

void func(int* ptr){
  //Yada-yada
}
int main(){
  int a[] = {1,2,3,4,5};
  func(a);
}

which worked out great. But then, I tried to do the following:

void func(int* ptr){
  //Yada-yada
}
int main(){
  int a[] = {1,2,3,4,5};
  func({1,32});
}

which returned an error saying

too many initializer values So I replaced it with

func({1});

which ended up with

a value of type "int" cannot be used to initialize an entity of type "int *"

So I'd like to know why this happens. Does the compiler not allocate space for an array that is not being used as an rvalue for a variable?? Because if it does, the expected result would be that ptr is passed the address of the first variable in either of the {1,32} or {1} cases.

Thanks in advance. P.S : Only reply to this if you intend to help. If you have comments to tell me to go read a book or something, I already am. But to the ones who actually want to be helpful, links to references are very much appreciated.

{1,32} is a std::initialized_list<int>, which is not convertible to an int *. — Sam Varshavchik
– Sam Varshavchik, Commented Oct 24, 2020 at 20:12
{1,32} is not an array. It doesn't have a type at all according to the C++ language specification. It's a syntactic construct that can be used to initialize objects. Sometimes, the properties of the object can be deduced from it, but those are the exceptions, not the rule. — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented Oct 24, 2020 at 20:17

eerorika · Accepted Answer · 2020-10-24 20:41:19Z

5

{1,32} is not "an actual array". It is a brace enclosed list of initialisers. The pointer parameter cannot be initialised with such list unless the list contains exactly one initaliser of a type that is convertible to the pointer.

edited Oct 24, 2020 at 20:41

answered Oct 24, 2020 at 20:17

eerorika

240k13 gold badges212 silver badges354 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Scheff's Cat Over a year ago

So, the 2nd case fails because a initializer list with multiple items is not compatible in general. The 3rd case fails instead because the list with 1 item would be compatible if the contained int would be compatible but it isn't. (The OP was lucky that the last snippet contained { 1 } but not { 0 } which had caused even more confusion.)

Collectives™ on Stack Overflow

Why does passing an actual array (not an array variable) as an argument to a function throw an error?

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related