Writing Device Drivers


void ASSERT(int expression)

ASSERT(9F) can be used to ensure that a condition is true at some point in the program. It is a macro whose use varies depending upon whether the compilation symbol DEBUG is defined. If DEBUG is not defined, the macro expands to nothing and the expression is not evaluated. If DEBUG is defined, the expression is evaluated and, if the value is zero, a message is printed to the system console and the system panics.

For example, if a driver pointer should be non-NULL and is not, the following assertion could be used to check the code:

	ASSERT(ptr != NULL);

If the driver is compiled with DEBUG defined and the assertion fails, a message is printed to the console and the system panics:

panic: assertion failed: ptr != NULL, file: driver.c, line: 56

Note -

Because ASSERT(9F) uses DEBUG, it is suggested that any conditional debugging code also be based on DEBUG, rather than on a driver symbol (such as MYDEBUG). Otherwise, for ASSERT(9F) to function properly, DEBUG must be defined whenever MYDEBUG is defined.

Assertions are an extremely valuable form of active documentation.