Re: using lParam if it's a pointer
- From: "Will Pearson" <will@xxxxxxxxxxxxx>
- To: <programmingblind@xxxxxxxxxxxxx>
- Date: Wed, 12 Dec 2007 11:04:37 -0000
Hi Tyler,
Yes, the first member declared is usually the first member in memory. Memory
layout can depend on the compiler and compiler options used, and so it is
probably worth checking your compiler's documentation to be sure.
The size of structs are fixed though, and their size depends on their
declaration in the header file in which they are declared. So, you can usually
get away with creating a struct of the type you need without looking at the
size member. There are some exceptions to this, such as when you may be
dealing with multiple structs and you are unsure which you will need in a given
situation and you need to then dynamically allocate them based on their size,
but these situations aren't encountered that often.
Will
----- Original Message -----
From: Littlefield, Tyler
To: programmingblind@xxxxxxxxxxxxx
Sent: Wednesday, December 12, 2007 3:35 AM
Subject: Re: using lParam if it's a pointer
thanks. will do.
Also. one last question.
If I have a struct like:
struct data{
int a,b,c,d,e,f,g;
};
will it order it in memory with a being first, g being last? I'm working on a
program that requires me to have an int size, and then read the first 4 bytes
to know how big the struct is.
Thanks,
Tyler Littlefield
Vertigo head coder.
"I can only please one person per day; Today doesn't seem like your day, and
tomorrow doesn't look to promising either."
"A life? Where can I download that at?"
Contact information:
email: tyler@xxxxxxxxxxxxx
skype: st8amnd127
aim: st8amnd2005
msn: tyler@xxxxxxxxxxxxx
----- Original Message -----
From: Will Pearson
To: programmingblind@xxxxxxxxxxxxx
Sent: Tuesday, December 11, 2007 4:56 PM
Subject: Re: using lParam if it's a pointer
Hi Tyler,
I suspect you will need to cast the lParam value. If you don't then the
compiler won't know that you are dealing with a structure and you will likely
get some compile errors. As the structure is a user defined data type then
there are likely no standard conversions.
Without a conversion the compiler will asumme that you are just dealing
with an unsigned 32-bit integer. LPARAM's is a typedef for LONG_PTR, and
LONG_PTR is in turn a typedef for long. As 32-bit unsigned numeric values
don't have members then tge compiler is likely to trow some compile errors.
Will
----- Original Message -----
From: Littlefield, Tyler
To: programmingblind@xxxxxxxxxxxxx
Sent: Tuesday, December 11, 2007 11:18 PM
Subject: Re: using lParam if it's a pointer
it says it's a pointer to a struct. I just want to get the data at like
lParam->foo;
Tyler Littlefield
Vertigo head coder.
"I can only please one person per day; Today doesn't seem like your day,
and tomorrow doesn't look to promising either."
"A life? Where can I download that at?"
Contact information:
email: tyler@xxxxxxxxxxxxx
skype: st8amnd127
aim: st8amnd2005
msn: tyler@xxxxxxxxxxxxx
----- Original Message -----
From: Ken Perry
To: programmingblind@xxxxxxxxxxxxx
Sent: Tuesday, December 11, 2007 7:30 AM
Subject: RE: using lParam if it's a pointer
This depends if your doing it in c++ or C but truthfully it probably
doesn't matter you should be able to do it with out a cast but it would give
you a warning it really depends on what your doing with it.
Ken
------------------------------------------------------------------------
From: programmingblind-bounce@xxxxxxxxxxxxx
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Littlefield, Tyler
Sent: Tuesday, December 11, 2007 5:27 AM
To: programmingblind@xxxxxxxxxxxxx
Subject: using lParam if it's a pointer
Hello list,
I've got a question.
I'm using a callback function, and lParam contains a pointer to a
struct of data.
I'm using like lParam->bla=32; do I need to cast lParam to the struct
first? (struct)lParam->bla=32;
Thanks,
Tyler Littlefield
Vertigo head coder.
"I can only please one person per day; Today doesn't seem like your
day, and tomorrow doesn't look to promising either."
"A life? Where can I download that at?"
Contact information:
email: tyler@xxxxxxxxxxxxx
skype: st8amnd127
aim: st8amnd2005
msn: tyler@xxxxxxxxxxxxx
Other related posts:
