When is a semicolon after } mandated in c/c++?

Question

if(...) {
  ...
}

It seems in the above case a ; is optional,when is a semicolon after } necessary in c/c++?

Solution 1

int a[2] = {1,2}, j = 5;

When initialization of array or structure are done with {} all the subsequent variables are declared after ,.

Edit: As you changed your question; ; is mandatory after the class, enum, initialization syntax declarations.

class A {};  // same for `struct
enum E {};   // enum class (c++0x)
int a[] = {1,2};  // array or object initialization

And as per comment by @rubenvb:

do {} while(condition);

Solution 2

A semicolon by itself is an empty statement, and you can add extra ones anywhere a statement is legal. Therfore it would be legal to put a semicolon right after the braces following your if, although it wouldn't be related to the if at all. The only place I can think of where a semicolon is required right after a bracket is after a class declaration in C++.

Solution 3

A semicolon after a close brace is manadatory if this is the end of a declaration. If it is the end of a block statement then no semicolon is needed, and if one is used, it makes an additional empty statement, which may be illegal if this is the middle of a if-else or a do-while (or a try-catch in C++)

---

Semicolons are required many places not after a close brace (at the end of any statement except a block-statement, at the end of any declaration, even if there is no }, in a for clause, etc, but generally braces are not involved in any of those.

Comments

[cpuer]

Why ; is required after class declaration but not after function declaration? C++ parser can't parse it without the ; in that case?

[cpuer]

any rational behind all these?

[Billy ONeal]

@cpuer: Because you can declare instances at the definition site. For example: struct ABC { int foo; int bar; } example; creates a variable named example of type ABC.

[Luc Danton]

@cpuer It's not a rationale but struct { int i; } s; is meaningful in C and C++. When you don't need the object(s) (here, s), then the ; remains.

[Billy ONeal]

@cpuer: For the class and enum examples, I explained in comments on Ernest's answer. For the array or object initializations, you need a semicolon simply because they are statements and all statements are terminated by ;s :)

[iammilind]

@cpuer, as @Luc said, since in C++ you can declare objects/pointers after the class/struct/enum declaration. Putting a ; helps the parser that one has to type the class name to declare any object. Since function / namespace' are not type; the ;` after them is not mandatory.

[rubenvb]

a do-while needs a semi-colon at the end!

[rubenvb]

Don't forget a do{ ... } while(...);

[Chris Dodd]

@rubenvb: if you try to put a ; after the } in a do-while loop, you'll get a syntax error.

[rubenvb]

but it is needed after the final ).

[tejasvi88]

@AdamRosenfield Are your aware of any other constructs like if-else, do-while and try-catch where semicolon after brace can be illegal?