function pointers

[GS Prabhu]

Hi,

I have a problem in using function pointers.The code is given below.

void taskcreate( void (*tsk) (void *stk),void *ptr,unsigned char x,unsigned char y);

task1(void *p)
{
---
---
}

main()
{
void *s;
unsigned char a,b;
---;
---;
createtask(tsak1,s,a,b);
---;
---;
}


void taskcreate( void (*tsk) (void *stk),void *ptr,unsigned char x,unsigned char y) // compiler error
{
-----;
-------;
}

compiler error is :"Function definition different from previous definition".

Then I changed both declaration and defintion of function "taskcreate" as

unsigned char taskcreate( void *tsk,void *ptr,unsigned char x,unsigned char y);


task1(void *p)
{
---;
---;
}

void (*t) (void *ptr);

main()
{
void *s;
unsigned char a,b;

t=task1; //*********
---;
---;
createtask(t,s,a,b);
---;
---;
}


unsigned char taskcreate( void *task,void *ptr,unsigned char x,unsigned char y)
{
void (*fnptr)( void *ptr);
fnptr=task;
(*fnptr) ( ptr);
-----;

-------;
}

Thsi method works well. But I need to call the function "taskcreate()" from main() by specifying the name of the function as given below.

main()
{
void *s;
unsigned char a,b;
---;
---;
createtask(task1,s,a,b); // Needed help
---;
---;
}


What are funtion pointer methods avialable in CCS compiler?.Otherwise please suggest me a method to solve this problem.


GS Prabhu,

[Ttelmah]

I suspect your problem is a common one with the CCS C, with regards to how 'voids' behave. In the original K&R defintions, a 'void', was a pseudonym for 'nothing', and a function returning 'void', could not return anything at all. Similarly, a function requiring a 'void', would not expect to receive any data at all. This is how 'voids' bechave in CCS.
Ansi C, then introduced the idea of a 'untyped' void. With this, a function could be defined to return a 'void', and could still return a value. When this was done, the returned data type, became a 'generic' type, which was automatically cast to fit the target. Void then becomes useable as a sort of 'undefined' type. This is not supported in CCS C.
Hence if you are using a pointer to a function, which may return something, it should be declared to return a type (for a pointer, and int16, rather than a unsigned char), and then 'cast' on use to the required type.

Best Wishes

[Trampas]

I suspect that the CCS compiler is broken and you can not use pointers to functions. I know I have tried and it does not work.

Trampas

[drh]

In the "common questions and answers" section of the reference manual,
"The compiler does not permit pointers to functions so that the complier can know at compile time the complete call tree. This is used to allocate memory for full RAM re-use".
_________________
David

[Mark]

[drh]

I guess that means that the trusty old "read the manual" can't be trusted anymore. Thanks CCS!
_________________
David