Can statements be written outside function body?

[Jian H. Li]

Hello,

As a beginner to C++, I need Your kind help to clarify the basic
concept. The sample C++ code as following:

int i; // A
i++; // B, error

int main()
{
i++; // C

return 0;
}

Though both are legal C++ statement, //A & //B are different in this
code. //A is correct but //B is wrong. The same as statement //A, //B
is legal also, but //B can't occur outside function body. After moving
//B to position //C, the error alert disapeared. PLEASE EXPLAIN WHY.

Thank you.

Your Sincerely
Joe Li

 

[Guillaume Brocker]

Hello,

As a beginner to C++, I need Your kind help to clarify the basic
concept. The sample C++ code as following:

int i; // A
i++; // B, error

int main()
{
i++; // C

return 0;
}

Though both are legal C++ statement, //A & //B are different in this
code. //A is correct but //B is wrong. The same as statement //A, //B
is legal also, but //B can't occur outside function body. After moving
//B to position //C, the error alert disapeared. PLEASE EXPLAIN WHY.

You can declare a variable in the global scope (outside any function or
class body), but must put statements that are not declarations into a
function body. That's how C and C++ have been designed.

 

[John Harrison]

Hello,

As a beginner to C++, I need Your kind help to clarify the basic
concept. The sample C++ code as following:

int i; // A
i++; // B, error

int main()
{
i++; // C

return 0;
}

Though both are legal C++ statement, //A & //B are different in this
code. //A is correct but //B is wrong. The same as statement //A, //B
is legal also, but //B can't occur outside function body. After moving
//B to position //C, the error alert disapeared. PLEASE EXPLAIN WHY.

Thank you.

Your Sincerely
Joe Li

Because you can't put statements outside a function body.

If you could then when do you think the statements should be executed?

john

 

[David Harmon]

If you could then when do you think the statements should be executed?

Well, obviously it should be executed at the same time it would be if
you had written:

int i;
int j = i++;

 

[Jian H. Li]

Because you can't put statements outside a function body.

If you could then when do you think the statements should be executed?

john

Not precise.
As shown below, code line //A is a legal statement outside a function body.

int i; // A
i++; // B, error

int main()
{
i++; // C

return 0;
}

 

[John Harrison]

"John Harrison" <[email protected]> wrote in message



Not precise.
As shown below, code line //A is a legal statement outside a function body.

int i; // A
i++; // B, error

int main()
{
i++; // C

return 0;
}

A is not a statement, it is a declaration. Declarations are legal outside of
function bodies, statements are not.

john

 

[osmium]

Not precise.
As shown below, code line file://A is a legal statement outside a function body.

int i; // A
i++; // B, error

int main()
{
i++; // C

return 0;
}

Statements *and* declarations both end in semicolons. Look at the BNF to
make this believable.

 

[Ron Natalie]

Statements *and* declarations both end in semicolons. Look at the BNF to
make this believable.

Some statements end in semicolons.

 

[Jian H. Li]

hello,

in iso/iec 14882, C++ standard, page 674~679 (A.5~A.7):



in A.5:
statement:
...
declaration-statement
...

declaration-statement:
block-declaration



A.6:
block-declaration:
simple-declaration
...

simple-declaration:
decl-specifier-seq(opt) init-declarator-list(opt) ;

decl-specifier-seq:
decl-specifier-seq(opt) decl-specifier

decl-specifier:
type-specifier
...

type-specifier:
simple-type-specifier
...

simple-type-specifier:
char
int
short
long
float
double
wchar_t
void
...



A.7:
init-declaration-list:
init-declarator
...

init-declarator:
declarator initializer(opt)

declarator:
direct-declarator
...

derect-declarator:
declarator-id
...

declarator-id:
id-expression
...



A.4:
id-expression:
unqualified-id
...

unqualified-id:
identifier
...

so, it's obvious "int i;" is a block-declaration, and also a statement.


Regards.
Jian H. Li

 

[Jian H. Li]

A is not a statement, it is a declaration. Declarations are legal outside of
function bodies, statements are not.

john

hello,

in iso/iec 14882, C++ standard, page 674~679 (A.5~A.7):



in A.5:
statement:
...
declaration-statement
...

declaration-statement:
block-declaration



A.6:
block-declaration:
simple-declaration
...

simple-declaration:
decl-specifier-seq(opt) init-declarator-list(opt) ;

decl-specifier-seq:
decl-specifier-seq(opt) decl-specifier

decl-specifier:
type-specifier
...

type-specifier:
simple-type-specifier
...

simple-type-specifier:
char
int
short
long
float
double
wchar_t
void
...



A.7:
init-declaration-list:
init-declarator
...

init-declarator:
declarator initializer(opt)

declarator:
direct-declarator
...

derect-declarator:
declarator-id
...

declarator-id:
id-expression
...



A.4:
id-expression:
unqualified-id
...

unqualified-id:
identifier
...

so, it's obvious "int i;" is a block-declaration, and also a statement.


Regards.
Jian H. Li

 

[Mike Wahler]

Because you can't put statements outside a function body.

If you could then when do you think the statements should be executed?

He probably believes "In the order they appear". Probably came
from BASIC.

-Mike

 

[Victor Bazarov]

You can, if they are declaration statements. The ++i is not
a statement by itself, it's an expression and it could be forced
to be evaluated, if you put it in a declaration/definition statement.

He probably believes "In the order they appear". Probably came
from BASIC.

But it is possible, generally, I believe. [this seems like a rather
old thread, though, maybe the question has already been answered...]

If you do

int i = 42;
int b = i++;

Then the (i++) part is going to be executed after the 'i's definition
and should probably do the trick...

Victor