C++ variable declation syntax

I recently came across this construct:
int(m);
which seems to be equivalent to:
int m;

Oddly, I have never seen this particular idiom before. Can someone point me to a reference where I can read the spec on this, or just explain directly? Does this also work in straight C?

Thanks,
ConfusedDeveloper

It is not an "idiom". It is just a redundant pair of parentheses. Grammatically, they can be there, but they serve no purpose.

Sometimes similar seemingly superfluous parentheses can be used to resolve ambiguity in C++ declarations, like

int a(int());

which declares a function can be turned into


int a((int()));

which is equivalent to

int a = int();

and defines a variable. But this is not exactly what you have in your case.

It's also used to cast. Like,

double m= 10.0;
int n= int(m);

In addition to other answers, sometimes declarator has to be parenthesized.<br>
For example:

struct A {};

struct B { A a; };

namespace N {
struct B { int a; };

void f()
{
A (::B::*p) = &::B::a; // this () cannot be omitted
}
}

If `()` is omitted in the above code, compiler recognizes a consecutive nested
name specifier `A::B` instead of `A` and `::B`, and will issue an error.<br>
This parenthesis is necessary, but sometimes leads to a misleading situation.

struct A {
int m;
A() {}
A( int ) {} // this isn't called
};

int i;

int main()
{
A(i); // this is a declaration
i.m = 1; // ok
}

In the above code, `A(i)` is a declaration(and also a definition in this case) of an object `i`,
instead of a constructor call expression with an `int` argument `i`.

Hope this helps.