open, creat, read, write, lseek and close
Are they all primitive?
:confused:
*Another Question: is there a different between a system call, and an i/o system call? (2 Replies)
Hi,
I'm new to UNIX system calls. Can someone share your knowledge as to how exactly system calls should be executed?
Can they be typed like commands such as mkdir on the terminal itself? Also, are there any websites which will show me an example of the output to expect when a system call like... (1 Reply)
Hello,
how would i be able to call ps in C programming?
thanks,
---------- Post updated at 01:39 AM ---------- Previous update was at 01:31 AM ----------
here's the complete system call, ps -o pid -p %d, getpit() (2 Replies)
Hi friends,
I have three questions.
1) What are system calls?
2) Is it necessary that system calls be in c language (in unix operating system)?
3) Importance of c language when programming in unix environment???
Looking forward to your wonderful replies!
... (2 Replies)
Hi friends,
I hope everyone is fine and doing well. I queried in my previous thread about the low-level qualities of C/C++ languages.I really thank you people for explaining, it was really helpful. One more ambiquity that I have in my mind is regarding the unix system calls like open, creat,... (1 Reply)
Discussion started by: gabam
1 Replies
LEARN ABOUT LINUX
varargs
varargs(3EXT) Extended Library Functions varargs(3EXT)NAME
varargs - handle variable argument list
SYNOPSIS
#include <varargs.h>
va_alist
va_dcl
va_list pvar;
void va_start(va_listpvar);
type va_arg(va_list pvar, type);
void va_end(va_list pvar);
DESCRIPTION
This set of macros allows portable procedures that accept variable argument lists to be written. Routines that have variable argument lists
(such as printf(3C)) but do not use varargs are inherently non-portable, as different machines use different argument-passing conventions.
va_alist is used as the parameter list in a function header.
va_dcl is a declaration for va_alist. No semicolon should follow va_dcl.
va_list is a type defined for the variable used to traverse the list.
va_start is called to initialize pvar to the beginning of the list.
va_arg will return the next argument in the list pointed to by pvar. type is the type the argument is expected to be. Different types can
be mixed, but it is up to the routine to know what type of argument is expected, as it cannot be determined at runtime.
va_end is used to clean up.
Multiple traversals, each bracketed by va_start and va_end, are possible.
EXAMPLES
Example 1: A sample program.
This example is a possible implementation of execl (see exec(2) ).
#include <unistd.h>
#include <varargs.h>
#define MAXARGS 100
/* execl is called by
execl(file, arg1, arg2, ..., (char *)0);
*/
execl(va_alist)
va_dcl
{
va_list ap;
char *file;
char *args[MAXARGS]; /* assumed big enough*/
int argno = 0;
va_start(ap);
file = va_arg(ap, char *);
while ((args[argno++] = va_arg(ap, char *)) != 0)
;
va_end(ap);
return execv(file, args);
}
SEE ALSO exec(2), printf(3C), vprintf(3C), stdarg(3EXT)NOTES
It is up to the calling routine to specify in some manner how many arguments there are, since it is not always possible to determine the
number of arguments from the stack frame. For example, execl is passed a zero pointer to signal the end of the list. printf can tell how
many arguments are there by the format.
It is non-portable to specify a second argument of char, short, or float to va_arg, since arguments seen by the called function are not
char, short, or float. C converts char and short arguments to int and converts float arguments to double before passing them to a function.
stdarg is the preferred interface.
SunOS 5.10 10 May 2002 varargs(3EXT)