•Subject: Re: Struggling with API QDFRTVFD

•Subject: Re: Struggling with API QDFRTVFD





Hi Barbara



You are a gem. Thanks for the lesson, I am still a C beginner, I admit.

I did not know how to cast types to a different type, wow.

Thanks again.



Frank

•From: Barbara Morris <bmorris@xxxxxxxxxx>

•Date: Tue, 19 Aug 2014 19:34:48 -0400

p_QDFFBASE + p_QDFFBASE->WDFFINOF

says to add the offset p_QDFFBASE->WDFFINOF to the pointer p_QDFFBASE.

In C, when you add an offset, say 5, to a pointer, it doesn't add 5 bytes

to the pointer,

it adds 5 multiples of the type of the pointer.

So if p_QDFFBASE is a pointer to a structure of length 32,

adding 5 to the pointer would actually add 5*32 bytes.

(char *) p_QDFFBASE

means to interpret p_QDFFBASE as a pointer to char,

no matter what type p_QDFFBASE actually is.

This forces the addition of the offset to be in bytes.

(QDFFINFO_t *) casts the resulting pointer to be a pointer to a QDFFINFO_t

structure,

which allows it to be assigned to p_QDFFINFO.

So the whole thing means to take the p_QDFFBASE pointer,

add p_QDFFBASE->WDFFINOF bytes to it, and assign it to p_QDFFINFO.

On 2014-08-19 09:10, Frank Kolmann wrote:

also I must admit I dont really know what this code means

p_QDFFINFO = (QDFFINFO_t *)((char *) p_QDFFBASE + p_QDFFBASE->WDFFINOF);

I know it sets a pointer to the data but what does

(QDFFINFO_t *)((char *) mean ?

•From: Barbara Morris <bmorris@xxxxxxxxxx>

•Date: Tue, 19 Aug 2014 19:44:46 -0400

The CZM0280 is telling you that you can't pass a char where a const char *

is wanted.

The reason that WDFARFNM works in the strncmp is that WDFARFNM is a char

array,

aka char *. WDFFFIOA is just a char.

So as Scott says, you can just compare it directly to 0x01.

This is an example of the compile error I am getting.

218 17 | if (strncmp(p_QDFFFINF->WDFFFIOA, Attrib, 1) == 0)

*=SEVERE==========> a - CZM0280 Function argument assignment between

types

"const char*" and "char" is not allowed.

...

However there are other uses of strncmp in the program that compile just

fine.