Compiler/Runtime uses of sizeof Post: 302962432

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Top Forums Programming Compiler/Runtime uses of sizeof Post 302962432 by GSalisbury on Monday 14th of December 2015 03:19:16 PM

12-14-2015

Registered User

Compiler/Runtime uses of sizeof

Ignoring other considerations for a moment and in general ...
Would there be a difference in result (dot oh or execution) of:

A.

Code:

   strncpy( a, b, sizeof(a) );

vs.

B.

Code:

   c = sizeof(a);
   strncpy( a, b, c );

My general understanding is (at least I think my understanding is) that in cases where something is inherently fixed in size then the compiler inserts the literal value of the size of the item at compile time as opposed to leaving an implicit run-time function call.

If my understanding is correct then it seems in scenario A. we'd have strncpy( a, b, 4 ) in one line of execute compared to two lines in B.: c = 4; strncpy( a, b, c ).

Is that not correct?
Am I missing something?
Thanks in advance for any comments.
Geo. Salisbury
Long Valley, NJ

Last edited by GSalisbury; 12-14-2015 at 05:04 PM.. Reason: Grammer

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LEARN ABOUT OPENDARWIN

fixadd

fixadd(3alleg4) 						  Allegro manual						   fixadd(3alleg4)

NAME

       fixadd - Safe function to add fixed point numbers clamping overflow. Allegro game programming library.

SYNOPSIS

       #include <allegro.h>

       fixed fixadd(fixed x, fixed y);

DESCRIPTION

       Although  fixed	point  numbers can be added with the normal '+' integer operator, that doesn't provide any protection against overflow. If
       overflow is a problem, you should use this function instead. It is slower than using integer operators, but if an overflow occurs  it  will
       set `errno' and clamp the result, rather than just letting it wrap. Example:

	  fixed result;
	  /* This will put 5035 into `result'. */
	  result = fixadd(itofix(5000), itofix(35));
	  /* Sets `errno' and puts -32768 into `result'. */
	  result = fixadd(itofix(-31000), itofix(-3000));
	  ASSERT(!errno); /* This will fail. */

RETURN VALUE

       Returns the clamped result of adding `x' to `y', setting `errno' to ERANGE if there was an overflow.

SEE ALSO

       fixsub(3alleg4), fixmul(3alleg4), fixdiv(3alleg4)

Allegro 							   version 4.4.2						   fixadd(3alleg4)