Thread: #error & #line

Don't you have a C book? If not, I'd suggest you buy one instead of asking how to use every single function and preprocessor directive. Also, consider using a search engine, which gives you hits like this and this, also things like this here and so on, and... well, you get the idea.

Quzah.

Originally Posted by codomaniac

Is this related to C. I afraid not! .

Actually, it is. But it's fairly easy to find out what you need, as I've illustrated with only a bit of typing into the nearest search engine.

Quzah.

>Is this related to C.
It is, as a matter of fact.

>please can you guys tell me how to use #error and #line.
#line gives you control over the macros __LINE__ and __FILE__. Those two are most often used in error reporting, but the need to reset them may arise in tool-generated source files that need to be associated at the line level with the original user-written file. A good example would be a preprocessor that makes signifigant changes yet still requires accurate symbolic debugging on the original source file. The syntax:

Code:

#line n filename

Makes changes to both __LINE__ and __FILE__. The syntax:

Code:

#line n

Only makes changes to __LINE__. Here's an example:

Code:

#include <stdio.h>

int
main(void)
{
  printf("This should be line 9: %d\t%s\n", __LINE__, __FILE__);
#line 12345 "Booga!"
  printf("This would be line 11 without #line: %d\t%s\n", __LINE__, __FILE__);

  return 0;
}

#error creates a compile-time error. It's usage is pretty obvious:

Code:

#if !defined(SOME_MACRO)
#  error "SOME_MACRO not defined"
#endif

>what does #pragma do?
In C89/90, #pragma is completely implementation dependent. For details on how it's used you need to look through your compiler's documentation. In C99, there are three standard pragmas, two for floating-point operations and one for complex number operations. Check your nearest C99 reference manual for details.