confused between declaration & definition

[arnuld]

1) int i = 3;
2.) int* pi;
3.) int* pi2 = &i
4.) char* pc;
5.) char c;
6) char c2 = 'a'
7.) char* pc2 = &c2
8.) char* ps = "Stroustrou p";
9.) extern double d;

2, 4 & 9 are the only declarations here. right ?

i know that 1, 3, 5, 6, 7, 8 are definitions but can we call them
declarations too?

Is 2 a legal declaration?

i dont understand the difference between 7 & 8.

[Alf P. Steinbach]

Re: confused between declaration & definition

* arnuld:

1) int i = 3;
2.) int* pi;
3.) int* pi2 = &i
4.) char* pc;
5.) char c;
6) char c2 = 'a'
7.) char* pc2 = &c2
8.) char* ps = "Stroustrou p";
9.) extern double d;
>
2, 4 & 9 are the only declarations here. right ?

All are declarations, but only 9 is a pure declaration (not a definition).

i know that 1, 3, 5, 6, 7, 8 are definitions but can we call them
declarations too?

Yes. Any definition is a declaration.

Is 2 a legal declaration?

Yes.

i dont understand the difference between 7 & 8.

7 declares a pointer to char and initializes it with the address of a
single char.

8 declares a pointer to char and initializes it with the address of the
first char in a zero-terminated sequence of chars (the string "Stroustrup ").

8 is bad form (because it means you can try to modify a string literal
without the compiler detecting that error). It's only allowed in order
to have backwards compatibility with old C. Except for interfacing to
old C code that requires it, you should write

char const* ps = "Stroustrup ";

or equivalently

const char* ps = "Stroustrup ";



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[Kai-Uwe Bux]

Re: confused between declaration & definition

arnuld wrote:

1) int i = 3;
2.) int* pi;
3.) int* pi2 = &i
4.) char* pc;
5.) char c;
6) char c2 = 'a'
7.) char* pc2 = &c2
8.) char* ps = "Stroustrou p";
9.) extern double d;
>
2, 4 & 9 are the only declarations here. right ?

2 and 4 look like definitions to me.

i know that 1, 3, 5, 6, 7, 8 are definitions but can we call them
declarations too?

Yes, the standard defines [3.1/2]:

A declaration is a definition unless it declares a function without
specifying the function?s body (8.4), it contains the extern specifier
(7.1.1) or a linkage-specification (7.5) and neither an initializer nor
a function-body, it declares a static data member in a class declaration
(9.4), it is a class name declaration (9.1), or it is a typedef
declaration (7.1.3), a using-declaration (7.3.3), or a using-directive
(7.3.4).

As you can see, every definition is a declaration.

Is 2 a legal declaration?

Looks legal to me. Did you run it by your compiler?

i dont understand the difference between 7 & 8.

8 is a special case since the right hand side is really const. Usually, when
you define a T*, you are allowed to modify the pointee; and any attempt to
define a T* so that it points to a (an array of) T char should fail. In
order to support C code, there are special provisions for char*.


Best

Kai-Uwe Bux

[Victor Bazarov]

Re: confused between declaration & definition

Alf P. Steinbach wrote:

* arnuld:

>1) int i = 3;
>2.) int* pi;
>3.) int* pi2 = &i
>4.) char* pc;
>5.) char c;
>6) char c2 = 'a'
>7.) char* pc2 = &c2
>8.) char* ps = "Stroustrou p";
>9.) extern double d;
>>
>2, 4 & 9 are the only declarations here. right ?

>
All are declarations, but only 9 is a pure declaration (not a
definition).

It depends on the context. 2, 4, 5, can also be declarations if
they happen to be inside a class definition.

>[..]

V
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