CODEWITHSUNDEEP
c++
Nikos Athanasiou
Nikos Athanasiou

Reputation: 31519

Function and struct having the same name in c++

The following code compiles in C++

struct foo
{
    int a, b;
};

struct foo foo()
{
    struct foo a;
    return a;
}

int main(void) {
    foo();
    return 0;
}
  1. Is it supposed to be allowed to have a struct and a function with the same name ?

  2. Since it compiles I then go on and try to declare an object of type foo. Is there a way? It seems impossible to do :

    foo a;   // error: expected ‘;’ before ‘a’
foo a{}; // error: expected ‘;’ before ‘a’
foo a(); // most vexing parse would kick in any way

Upvotes: 10

Views: 6846

Answers (5)

songyuanyao
songyuanyao

Reputation: 172904

From The.C++.Programming.Language.Special.Edition $A.8:

To preserve C compatibility, a class and a non-class of the same name can be declared in the same scope ($5.7). For example:

struct stat { /* ... */ };
int stat(char * name, struct stat * buf);

In this case, the plain name (stat) is the name of the non-class. The class must be referred to using a class-key prefix .

Upvotes: 1

Shafik Yaghmour
Shafik Yaghmour

Reputation: 158469

Yes, this is allowed we can see this by going to draft C++ standard section 3.3.10 Name hiding paragraph 2 and it says (emphasis mine):

A class name (9.1) or enumeration name (7.2) can be hidden by the name of a variable, data member, function, or enumerator declared in the same scope. If a class or enumeration name and a variable, data member, function, or enumerator are declared in the same scope (in any order) with the same name, the class or enumeration name is hidden wherever the variable, data member, function, or enumerator name is visible.

In this case using struct in the declaration would fix your issue:

struct foo a;

Upvotes: 10

Deduplicator
Deduplicator

Reputation: 45654

Just do it like you would in C, using:

struct foo a;

You might even initialise it like this:

struct foo a{};
struct foo a = {0};

A workaround would be using a typedef, thus avoiding any ambiguity and other difficulties:

typedef struct foo s_foo;

Upvotes: 2

kfsone
kfsone

Reputation: 24249

Yes, you can, but it's a really bad pattern to get into.

struct foo
{
};

foo foo(foo& f)
{
    return f;
}

int main()
{
    struct foo f;
    foo(f);
    return 0;
}

See livedemo: http://ideone.com/kRK19f

The trick was to specify struct foo when we wanted to get at the type. Note that, until you create this ambiguity, it's actually not necessary to keep saying struct, this isn't C (as in the line foo foo(foo& f)).

Most developers choose a camel casing pattern, e.g they use an upper case letter to distinguish type names and a lowercase letter for a function name:

struct Foo
{
};

Foo foo(); // no ambiguity.

Back in Microsoft's prime, many Windows developers acquired the habit of prefixing struct/class definitions, the definition of a class of thing if you will, with a capital C

struct CFoo
{
};

Now, even if you want to use upper-case first letters for your function names, there is no ambiguity.

Upvotes: 1

phyrrus9
phyrrus9

Reputation: 1467

Usually a bad habbit to do something like that. I would name it foo_s or whatever to distinguish it from the function. Other than that, there isn't really a way of doing it.

In C this is possible, since it requires

struct foo

instead of just

foo

as the type name (unless it is typedef'd)

Upvotes: 1

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