I am learning posix api. I could not get logic behind names used by posix api
e.g.
S_IRUSR, S_IRUSR
What does What does S stand for? I can get R and W are for read and write. But what naming convention followed by POSIX ?
Its just an example. What about other names ? Just like Win32 follow Hungarian Notation for naming what does POSIX follow for their naming ? For standard like POSIX there must be documentation for it. Can somebody please link it.
thanks for any clue .
I am not sure if they have any meaning except that they're in sys/stat.h, so the S may stand for "stat".
I tried doing some detective work, for example, the IEEE Std 1003.1, 2004 Edition entry for sys/stat.h says this: First released in Issue 1. Derived from Issue 1 of the SVID.
Then, the Developer Specs for System V Application Binary Interface (see Volume 1a [pdf]), page 95, and even that has names beginning with S_. I haven't been able to go further back than this.
About your question in general: much of it is history. For example, creat() is in POSIX, but the name comes from history. Many of POSIX function names (and behavior) comes from the C standard. In fact, their description usually have text like:
The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to the ISO C standard.
I think the only way to find any logic behind the POSIX API is to read the history of Unix.
The following may help:
Alok is correct. See the specification for sys/stat.h. If you were to write your own stat() / statvfs() implementation (very common in ports that make non-posix programs work on POSIX hosts) you would prefix it with something else, i.e. Z_IRUSR.
While I don't have a list handy, I am quite certain that some C implementations provide several choices for sys/stat, S_ giving you typical POSIX behavior and (X) giving you something else. I have not seen that in a long time, though, which is why I can't quite recollect where I ran into it.
The leading S_ is just to identify what structure/function the constant goes with.
From <sys\stat.h>, the constants S_IRUSR, S_IWUSR, etc are possible values for the st_mode member for struct stat (used in stat() and friends). All the members of struct stat start with the prefix st_, and there are several stat-related macros that also start with S_. The convention is merely there to make matching structure names, member names, and constants easier.