Initialization of Structs - Typedefs

[Mahendra]

I have the following structs -

15 typedef struct pSimple {
16 char *key;
17 char *val;
18 } pSimple, *pSimple_ptr;
19
20 typedef struct pComplex {
21 char *name;
22 int value;
23 } pComplex, *pComplex_ptr;
24
25 typedef struct pNode {
26 char *nodeId;
27 struct pSimple *semStats;
28 struct pComplex *sysStats;
29 } pNode, *pNode_ptr;

Now somewhere in my main() i do -

pNode data;

and then call generate_data(& data); where i want to initialize the
"data". Now the question i have is -

1. When i do- pNode data, does it allocate struct pNode ? If yes, it is
in stack ? If not what exactly does it does ? Can i just use &data to
initialize the struct pNode or do i have to allocate heap memory for it ?

Thanks
Mahendra

[Eric Sosman]

Re: Initialization of Structs - Typedefs

Barry Schwarz wrote:

On Mon, 03 Nov 2008 11:54:16 -0500, Eric Sosman <Eric.Sosman@su n.com>
wrote:
>

>Mahendra wrote:

>>I have the following structs -
>>[...]
>> 25 typedef struct pNode {
>> 26 char *nodeId;
>> 27 struct pSimple *semStats;
>> 28 struct pComplex *sysStats;
>> 29 } pNode, *pNode_ptr;
>>>
>>Now somewhere in my main() i do -
>>>
>>pNode data;
>>>
>>and then call generate_data(& data); where i want to initialize the
>>"data". Now the question i have is -
>>>
>>1. When i do- pNode data, does it allocate struct pNode ? If yes, it is
>>in stack ? If not what exactly does it does ? Can i just use &data to
>>initialize the struct pNode or do i have to allocate heap memory for it ?

> Yes, probably, doesn't matter, yes, no.
>>
> Yes, the declaration allocates storage for the thing declared,

>
definition and defined instead of declaration and declared

Given the absence of the `extern' keyword, I stand by
my nomenclature.

--
Eric Sosman
esosman@ieee-dot-org.invalid

[Barry Schwarz]

Re: Initialization of Structs - Typedefs

On Mon, 03 Nov 2008 20:41:58 -0500, Eric Sosman
<esosman@ieee-dot-org.invalidwrot e:

>Barry Schwarz wrote:

>On Mon, 03 Nov 2008 11:54:16 -0500, Eric Sosman <Eric.Sosman@su n.com>
>wrote:
>>

>>Mahendra wrote:
>>>I have the following structs -
>>>[...]
>>> 25 typedef struct pNode {
>>> 26 char *nodeId;
>>> 27 struct pSimple *semStats;
>>> 28 struct pComplex *sysStats;
>>> 29 } pNode, *pNode_ptr;
>>>>
>>>Now somewhere in my main() i do -
>>>>
>>>pNode data;
>>>>
>>>and then call generate_data(& data); where i want to initialize the
>>>"data". Now the question i have is -
>>>>
>>>1. When i do- pNode data, does it allocate struct pNode ? If yes, it is
>>>in stack ? If not what exactly does it does ? Can i just use &data to
>>>initialize the struct pNode or do i have to allocate heap memory for it ?
>> Yes, probably, doesn't matter, yes, no.
>>>
>> Yes, the declaration allocates storage for the thing declared,

>>
>definition and defined instead of declaration and declared

>
Given the absence of the `extern' keyword, I stand by
>my nomenclature.

But if extern had been part of the code, it would definitely be a
declaration and not a definition. And of course it would not have
allocated storage. That it did allocate storage is one of the clear
distinctions between declarations and definitions.

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