Newsgroup: comp.lang.c

August Karlstrom wrote:
> Does anyone know why some of the functions in time.h use pointers to 
> constant objects of type time_t when time_t is an aritmetic type. Why is 
> e.g. ctime declared as
> 
>    char* ctime(const time_t* tp);
> 
> and not as
> 
>    char* ctime(time_t t);

My guess is that this is an implementation decision related to the 
environment where C has its roots.  In the Seventh Edition Unix (and 
probably also in earlier versions), time_t is implemented as a long
<http://minnie.tuhs.org/UnixTree/V7/usr/include/sys/types.h.html>.  On a 
PDP-11 where that 1979 version of Unix run, passing as an argument a 16 
bit pointer to a 32 bit long was probably more efficient than passing 
the actual 32 bit value.

-- 
Diomidis Spinellis
Code Quality: The Open Source Perspective (Addison-Wesley 2006)
http://www.spinellis.gr/codequality?clc

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