Petzold exaples with PellesC

[ly47]

Hi

I'm transferring examples from Petzold Book to be compiled with PellesC.
(There are 23 chapters, so far I did only 15 chapters).
There is a problem with chapter 15- DibSect  example.
I'm getting this error message:
//
C:\C\Projects\Petzold\p15-DibSect\DibSect.c(104): error #2140: Type error in argument 4 to 'CreateDIBSection'; expected 'void * *' but found 'unsigned char * *'.
*** Error code: 1 ***
//
How to fix it ?
Thanks
ly

[frankie]

With a cast to void **:

Code Select Expand

hBitmap = CreateDIBSection (NULL, pbmi, DIB_RGB_COLORS, (void **)&pBits, NULL, 0) ;    //Line 104
PellesC unlike MSVC makes strict types checking as required by C standards.
MSVC is well known to be very lazy about these issues....

[ly47]

Hi frankie
Thanks a lot, now it works.
ly

[neo313]

This is a good time to make sure your code adheres to the c standard. While Pelles and VisualStudio don't follow aliasing rules, other compilers might( gcc does ), causing your code to produce undefined behavior on such compilers.

If a function requires a void** type, then the only standard compatible way is to pass that type. Types char** and void** are not compatible, such types may not alias, even with the cast.

So the correct solution would be:

Code Select Expand


    void* temp = NULL ;
    hBitmap = CreateDIBSection (NULL, pbmi, DIB_RGB_COLORS, &temp, NULL, 0) ;
    pBits = temp ;


[ly47]

Hi neo313
Thanks for your explanation.
ly

[frankie]

If a function requires a void** type, then the only standard compatible way is to pass that type. Types char** and void** are not compatible, such types may not alias, even with the cast.

What means???

[neo313]

Hi neo313
Thanks for your explanation.
ly

No problem,

neo