function parameter of array of T "decaying" to pointer to T?

Question

If I have a function...

void f(int x[3]) {}

...is this distinguishable from a function...

void f(int* x) {}

If not, where in the standard does it address this issue?

Clearly there are array-to-pointer standard conversions, but I don't think they apply here?

I seem to remember language which said something to this effect, but can't seem to find it.

$ cat t.cc
void f(int x[3]) {}

void f(int* x) {}

$ g++ t.cc
t.cc: In function ‘void f(int*)’:
t.cc:3:6: error: redefinition of ‘void f(int*)’
 void f(int* x) {}
      ^
t.cc:1:6: note: ‘void f(int*)’ previously defined here
 void f(int x[3]) {}
      ^

Woudln't you be able to answer your first question by compiling that? — gsamaras, Nov 20 '18 at 14:31
@gsamaras: I'm pretty sure the first answer is no, I'm looking for the standard reference. — Andrew Tomazos, Nov 20 '18 at 14:32
A rhetorical question then Tomazos..:) Does [this](https://stackoverflow.com/a/1462103/2411320) answer your 2nd question? — gsamaras, Nov 20 '18 at 14:34
*"I'm looking for the standard reference"* Then I suggest tagging with `language-lawyer`. — HolyBlackCat, Nov 20 '18 at 14:36

score 4 · Accepted Answer · edited Jun 20 '20 at 09:12

If I have a function...
void f(int x[3]) {}
...is this distinguishable from a function...
void f(int* x) {}

No. Those declarations are equivalent.

Standard draft:

[dcl.fct]

The type of a function is determined using the following rules. The type of each parameter (including function parameter packs) is determined from its own decl-specifier-seq and declarator. After determining the type of each parameter, any parameter of type “array of T” or of function type T is adjusted to be “pointer to T”. ...

This rule complements the array decaying rule. Array decaying allows calling a function with - apparently - an array argument, while this rule allows declaring a function with - apparently - an array argument, while actually what is passed is a pointer. These rules stem from the C heritage of the language. Same with function to pointer decaying.

@AndrewTomazos note that the numbering of § paragraphs often change between standard versions, which is why I avoid them in my anwers. Sometimes rules migrate under different named sections too, but that's more uncommon. — eerorika, Nov 20 '18 at 14:50

score 3 · Answer 2 · answered Nov 20 '18 at 14:37

3

From [dcl.fct§5] (emphasis mine):

The type of a function is determined using the following rules. The type of each parameter (including function parameter packs) is determined from its own decl-specifier-seq and declarator. After determining the type of each parameter, any parameter of type “array of T” or of function type T is adjusted to be “pointer to T”.

answered Nov 20 '18 at 14:37

Quentin

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I was curious, so I checked the timestamps. On the second. DAMMIT indeed :) – StoryTeller - Unslander Monica Nov 20 '18 at 14:39

score 2 · Answer 3 · answered Nov 20 '18 at 14:37

2

It's described in the specification of function declarators

[dcl.fct]

5 [...] After determining the type of each parameter, any parameter of type “array of T” or of function type T is adjusted to be “pointer to T”. [...]

answered Nov 20 '18 at 14:37

StoryTeller - Unslander Monica

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DAMMIT. ------- – Quentin Nov 20 '18 at 14:37
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@Quentin - Hey, it was you who dubbed me a hash table once ;) – StoryTeller - Unslander Monica Nov 20 '18 at 14:38

function parameter of array of T "decaying" to pointer to T?

3 Answers3