#if

[pbchaudhari]

Does the standard functions defined in header files work in #if directives?

[Ayesha Siddiqua]

#if a conditional compilation directive.
Syntax-#if(constant_expression)
#else
#endif
The compiler only compiles the lines that follows the #if directive wen constant_expression evaluates to non-zero.
Otherwise the compiler skips the lines that follow until it encounters the matching #else or #endif.
If the expression evaluates to false and there is a matching #else, the lines b/n the #else and the #endif are compiled.
#if directive can b nested, but matching #else and #endif directives must b in da same file as da #if.

[sk_seeker]

Does the standard functions defined in header files work in #if directives?

Question is a bit vague: so treat the answer with a grain of salt.

It depends on the expression in #ifdef EXPR.

For example, if it is #ifdef __KERNEL, then standard user mode functions will not work. For example, fprintf and other user mode libc functions will not work.

Hope that helps.

[karna rao]

Generally if is condition.Condition mean it will controls the depended statements one or more than.but #if this is also control statement but #(symbol) is used for preprocessors symbol.In this case we will define that condition in statement form afer we will use that name.
Ex>#defeine karna i>j
#if karna
printf ("i is big");
#else
printf("j is big");
#end if