Do I use #define or const?
Use Both. #defines can be included in header files and included in many files. But const variables tend to be limited to one file at a time.Built In Preprocessor Names
These four names are built into the C preprocessor. They may come in handy for tracking down bugs.Each starts and ends with two underscores.
- __LINE__ This is an integer that has the current source file line number.
- __FILE__ This is the name of the current source code file as a string.
- __DATE__ This is the PC's current date, as a string like Aug 17 2006.
- __TIME__ This is the PC's current time in string "hh:mm:ss" format.
#include <stdio.h> int main() {Note that I've used __LINE__ three times, once as a #define. The output of this is
#define c __LINE__
const int d = __LINE__;
printf("Value of Line is %i\n\r",__LINE__) ;
printf("Value of Filename is %s\n\r",__FILE__) ;
printf("Value of c is %i\n\r",c) ;
printf("Value of d is %i\n\r",d) ;
printf("Today's date and time is %s %s\n\r",__DATE__,__TIME__) ;
return 0;
}
Value of Line is 7The value of __LINE__ changed between the three uses of it. Notice that the #define for c was before the const int d but because c was substituted in line 9, it had that value.
Value of Filename is example3.c
Value of c is 9
Value of d is 6
Today's date and time is Aug 17 2006 21:15:50
That completes this lesson. In the next lesson, you'll learn about Control Statements.
