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Hello together,
I'm coding a simple UART-Application on the MCBSTM32 eval board and have problems with the preprocessor directives. I studied the whole documentation here and I'm pretty sure I'm coding in a common way, but still I can't compile my program. These are the very first lines of my main header file:
#ifndef ___MAIN_H_ #define ___MAIN_H_ #endif #undef EX #ifndef ___MAIN_C_ #define EX extern #else #define EX #endif
And my variables a coded that way:
EX unsigned int ui_TxFrameCounter;
When compiling the program, I get the error code "L6200E: symbol multiply defined" for my variables, because of including the header to other files. I want to declare the variables "extern" for the other header files. Could somebody help me? Would be nice. Geetings
I'm pretty sure I'm coding in a common way
More to the point, you're following common, yet bad advice. This whole "EX" machinery (more commonly seen with "EXTERN" as the macro name) is a waste of energy, and it tends to break in quite nasty ways as soon as people start trying to extend it to explicitly initialized variables. In the end, this "trick" will hurt worse than the problem it claims to solve.
#ifndef ___MAIN_H_ #define ___MAIN_H_ #endif
That #endif is entirely in the wrong place for this work as a multiple inclusion guard.
I think that's what the 'C' FAQ means when they say,
"It is possible to use preprocessor tricks ... but it's not clear if this is worth the trouble"
c-faq.com/.../decldef.html
Thanks for your comments! So what would you prefer? How would you solve the problem with the global variables?
I'm tryin it at the moment with this code in main.h:
#define MAIN_H_ #undef EX #ifndef MAIN_C_ #define EX extern #else #define EX //Prototypes and variable declarations... //... #endif //at the end of file
But this doesn't work too. I still need to declarate the variables in the main.c , otherwise they are not known. Greetings
Like this ("include guard" omitted for clarity):
The header file contains only straightforward extern declarations:
// main.h extern char tom; extern int ***; extern long harry;
main.c contains the definitions and includes the header:
// main.c #include "main.h" char tom; int ***; long harry;
Including the header here is important - it's what allows the compiler to detect any discrepancies!
Other .c files just include the header:
// other.c #include "main.h" // code can reference tom, ***, and/or harry...
Again, see: c-faq.com/.../decldef.html
If you still want to pursue the preprocessor business, the first thing to do is to examine the preprocessor output - see Andy's Handy Hint for Debugging Preprocessor Problems here: www.8052.com/.../read.phtml (it is not specific to 8052).
How would you solve the problem with the global variables?
By rejecting the conclusion that there were any problem to be solved there.