Pragmatic directives: Difference between revisions

=={{header|C}}==

The C Preprocessor is well explained on the [https://gcc.gnu.org/onlinedocs/cpp/index.html#Top GNU] site. The pragma page is [https://gcc.gnu.org/onlinedocs/cpp/Pragmas.html here].

<lang C>

/*Abhishek Ghosh, 7th October 2017*/

/*Almost every C program has the below line,

the #include preprocessor directive is used to

instruct the compiler which files to load before compiling the program.

All preprocessor commands begin with #

*/

#include<stdio.h>

/*The #define preprocessor directive is often used to create abbreviations for code segments*/

#define Hi printf("Hi There.");

/*It can be used, or misused, for rather innovative uses*/

#define start int main(){

#define end return 0;}

start

Hi

/*And here's the nice part, want your compiler to talk to you ?

Just use the #warning pragma if you are using a C99 compliant compiler

like GCC*/

#warning "Don't you have anything better to do ?"

#ifdef __unix__

#warning "What are you doing still working on Unix ?"

printf("\nThis is an Unix system.");

#elif _WIN32

#warning "You couldn't afford a 64 bit ?"

printf("\nThis is a 32 bit Windows system.");

#elif _WIN64

#warning "You couldn't afford an Apple ?"

printf("\nThis is a 64 bit Windows system.");

#endif

end

/*Enlightened ?*/

</lang>

On compilation and output, the compiler type is detected rather than the actual OS :

<pre>

C:\rosettaCode>gcc pragmatic.c

pragmatic.c:22:2: warning: #warning "Don't you have anything better to do ?"

pragmatic.c:28:2: warning: #warning "You couldn't afford a 64 bit ?"

C:\rosettaCode>a

Hi There.

This is a 32 bit Windows system.

</pre>