I am porting some code to an 8051. (header.h)
typedef int (Writer) (int , u_char * , u_char , size_t , u_char * , int *) reentrant;
Writer bob;
. . . int bob(int val1, u_char * dat1, u_char dat2, size_t val2, u_char * dat3, int *pval) reentrant { }
//Comment out Writer bob; int (bob)(int val1, u_char * dat1, u_char dat2, size_t val2, u_char * dat3, int *pval) reentrant;
The problem is not really the typedef itself --- which is a function type, rather than the function pointer type your subject alludes to. The problem is how you use it.
extern Writer bob;
The .h file provides a "prototype" of a function to be defined elsewhere. The redefinition warning means that when you actually define the function in the .c file, it does not match a previously seen declaration (typically in a .h file). While you've run into this problem with the reentrant attribute, it applies to any change in function signature. That is, .h: void MyFunction (long a); .c: void MyFunction (short a); would produce a redefinition warning. The .h file should always match the actual definition of the function, lest you confuse seperately-compiled callers.
The .h file provides a "prototype" of a function to be defined elsewhere. That what it should do, for ordinary functions. But the case at hand is different, because
"the proper way of making sure of this is to always include the module's header file into its own .c file." Yep - that's what I always say!
Thank you for the help. Extern did not improve anything unforunately. It appears that it is coded this way because the function is also passed within structures and other functions. In this way, we are not rewriting all of the details of the function pointer. This style is being used quite often in the code. I only seem to have a problem when I am forced to define the function as reentrant(too many arguments). For example:
(header.h) typedef int (Writer) (int); Writer bob;
(header.c) int bob(int a){ ... }
"I am only having the problem when the function is too large and I have to redefine it as reentrant." Why does the Size of the function affect the need for the reentrant attribute?