c++ - operator new syntax for array of pointers -

c++ - operator new syntax for array of pointers -

i have run next code

int main() { int **objects; objects=new (int(*[10])); // seems equal new int*[10]; delete[] objects; homecoming 0; }

i have not managed parse line "new (int(*[10]))". used standard syntax "new int*[10]" , totally surprised 1 above.

could explain me why "new (int(*[10]))" right , same "new int*[10]"?

here 2 grammatical constructions @ work, straight [c++11: 5.3.4]:

new-expression: ::optnew new-placementopt new-type-id new-initializeropt ::optnew new-placementopt( type-id ) new-initializeropt

you're used former have encountered latter. let's take closer @ one; type-id , how differ new-type-id?

[c++11: 5.3.4/3]: new-type-id in new-expression longest possible sequence of new-declarators. [ note: prevents ambiguities between declarator operators &, &&, *, , [] , look counterparts. —end note ] [ example:

new int * i; // syntax error: parsed (new int*) i, not (new int)*i

the * pointer declarator , not multiplication operator. —end illustration ]

so, see, why new (int(*[10])) valid new int(*[10]) not: outer parenthesis allows 5.3.4/3 kick in.

this addressed in next passage, validity of inner parenthesis in illustration very similar yours:

[c++11: 5.3.4/4]: [ note: parentheses in new-type-id of new-expression can have surprising effects. [ example:

new int(*[10])(); // error

is ill-formed because binding is

(new int) (*[10])(); // error

instead, explicitly parenthesized version of new operator can used create objects of compound types (3.9.2):

new (int (*[10])());

allocates array of 10 pointers functions (taking no argument , returning int.) —end illustration ]

—end note ]

in case, although using pointers rather pointers-to-functions (note additional () in above quote examples), int (*[10]) still compound type , same logic applies.

finally, int (*[10]) same int* [10] because it is: that's how syntax of type-id constructions works:

<tomalak> << type_desc<int (*[10])>; <geordi> array of 10 pointers integers <tomalak> << type_desc<int* [10]>; <geordi> same output.

(using geordi)

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