Please discuss a change in queue.c

nobody wrote on Monday, February 14, 2005:

Hi everybody,

I’m preparing a port to the C167 microcontroller (Infineon) to be published here. Now I encountered the following problem with the Keil IDE.

As I use the EC++ - Compiler supplied in the actual version of Keil’s IDE there’s a problem in queue.c. The line
typedef xQUEUE * xQueueHandle;
makes a different definition as given in queue.h
typedef void * xQueueHandle;

This is used to hide the xQUEUE-structure from the user. So far so good. The EC++ - Compiler now tries to find a overloaded function with the queue.h - definition. In queue.c there’s only xQUEUE definition. A linker-error (unresolved symbol) is the result.

My suggestion : Let’s change the definition of xQueueHandle in queue.c to void * too. When one does this, almost any occurence of the variable “pxQueue” in queue.c has to be changed to “((xQUEUE *)pxQueue)”.

I did this and it solved all problems with queue.c and queue.h. Please discuss this suggestion. I offer you my version of the v2.6.0 queue.c with this changes (~50 items to change !).

Thanks, Daniel Braun
eMail :

nobody wrote on Monday, February 14, 2005:

I presume this is a problem because you are using a C++ compiler rather than a C compiler.

Is it possible to designate the source files as C files with

extern "C"

around all the code in the file?  Alternatively is there a way from the project file to request that these particular files should be compiled as C files?

rtel wrote on Monday, February 14, 2005:

I am not surprised this is a problem with a C++ compiler.  In fact, I am surprised that none of the C compiler used have complained so far.

Do you find the same problem with the pxCurrentTCB variable?  This is defined both as tskTCB* and void* within the tasks.c and port.c files respectively.

As you say, this will require a lot of changes and probably effects the semaphore macros also.  There are two issues:

1) Readability.  There is a lot of casting already.  This is necessitated by the number of compilers used - each likes things slightly different.  More casting will reduce readability, BUT a #define could be used to prevent this.  eg

#define QUEUE ( ( xQUEUE *)pxQueue)

then just replace the pxQueue’s within the function bodies with QUEUE.

2) As just mentioned, each compiler likes things a little differently.  I would have to make sure that any changes are accepted by all the compilers.

Can the compiler be made to compiler files with a .c extension as C files, rather than C++?


nobody wrote on Monday, February 14, 2005:

Hi again,

1. if all C-functions defined so far have to be declared as extern C {…} one has to change the header queue.h (and others)

2. my proposal for casting should not affect other compilers - it should be possible to compile it with any C/C++ - Compiler.

3. I think Richard’s method (1) can enhance readability to a level comparable to today’s code.

4. I have now tested the modified queue.c (with standard queue.h) and found no problems.

Do you want the code to test it - where should I send it to ?

Regards, Daniel.

rtel wrote on Monday, February 14, 2005:

Hi Daniel,

Can you send it to the email address listed on the site "contacts" page.  I will check it out with the other compilers.