Meaning of Packed and Local types

[Muralidhar]

Hi all,

I saw in one function that its return type was written as PACKED...I wasnt
sure what that would mean. Any pointers on this?

Also, what is the significance of specifically mentioning the LOCAL to a
function definition when it will be a local function without the access of
its declaration?

Thanks
Murali

 

[Eric Sosman]

Hi all,

I saw in one function that its return type was written as PACKED...I wasnt
sure what that would mean. Any pointers on this?

Also, what is the significance of specifically mentioning the LOCAL to a
function definition when it will be a local function without the access of
its declaration?

Neither PACKED nor LOCAL has any meaning in "out of
the box" C. They are probably #define'd as macros that
expand to something meaningful, possibly compiler-specific.

 

[Christian Staudenmayer]

Eric Sosman is right, this isn't part of the Standard. However, if you
were wondering what "Packed" means, it usually describes a way to store
several values in one variable. For example, you might have a program
that needs millions of "boolean" values (0 or 1). Using char for that
would be a waste of 7/8th of the memory. You could now write a function
that "packs" 8 boolean values into one char (since char is guaranteed to
be at least 8 bit wide).

Greetings, Chris

 

[Trent Buck]

To follow up on what others have said, packed is a variable attribute
provided by the GCC[0] as an extension. This is documented in the
(tex)info manual, which if installed can be accessed via the command:

info gcc 'C Extensions' 'Variable Attributes'

-trent

[0] And possibly others, I don't know.

 

[Ben Pfaff]

To follow up on what others have said, packed is a variable attribute
provided by the GCC[0] as an extension.

But it isn't written PACKED. There is probably macro trickery
going on here.

 

[Muralidhar]

Yup...the GCC reference for that was __packed.

I guess it must be a typedef since the compiler/linker has to know when to
pack ...am I right?

murali

To follow up on what others have said, packed is a variable attribute
provided by the GCC[0] as an extension.

But it isn't written PACKED. There is probably macro trickery
going on here.
--
int main(void){char p[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.\
\n",*q="kl BIcNBFr.NKEzjwCIxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+=strchr(p,*q++)-p;if(i>=(int)sizeof p)i-=sizeof p-1;putchar(p\
);}return 0;}

 

[pete]

Yup...the GCC reference for that was __packed.

I guess it must be a typedef since the compiler/linker
has to know when to pack ...am I right?

I'm guessing that it's a macro defined somewhere in the source code.