•Subject: Re: Struggling with API QDFRTVFD

[Frank Kolmann <fkolmann@xxxxxxxxx>]

•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.