Difference between various functions

[SDZ]

Could somebody explain in simple forms, what is/are the difference(s) between

- scanf and sscanf and ssscanf
- printf and sprintf
- open and fopen

Thanks in advance,
SDZ

[Joona I Palaste]

Re: Difference between various functions

SDZ <sainyuja@hotma il.com> scribbled the following:[color=blue]
> Could somebody explain in simple forms, what is/are the difference(s) between[/color]
[color=blue]
> - scanf and sscanf and ssscanf[/color]

scanf reads from stdin, sscanf from a string. ssscanf doesn't exist.
[color=blue]
> - printf and sprintf[/color]

printf prints into stdout, sprintf into a string.
[color=blue]
> - open and fopen[/color]

open doesn't exist. fopen opens a file.

--
/-- Joona Palaste (palaste@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"It was, er, quite bookish."
- Horace Boothroyd

[Paulo PEREIRA]

Re: Difference between various functions

On 2004-06-14, Joona I Palaste <palaste@cc.hel sinki.fi> wrote:[color=blue]
> SDZ <sainyuja@hotma il.com> scribbled the following:[color=green]
>> Could somebody explain in simple forms, what is/are the difference(s) between[/color]
>[color=green]
>> - scanf and sscanf and ssscanf[/color]
>
> scanf reads from stdin, sscanf from a string. ssscanf doesn't exist.
>[color=green]
>> - printf and sprintf[/color]
>
> printf prints into stdout, sprintf into a string.
>[color=green]
>> - open and fopen[/color]
>
> open doesn't exist. fopen opens a file.
>[/color]

open is an UNIX system call for opening files. Not related to ISO C.

--
"Computers are useless. They can only give you answers"
- Pablo Picasso

[paulo-pereira dot perso at wanadoo dot fr]

[Default User]

Re: Difference between various functions

SDZ wrote:[color=blue]
>
> Could somebody explain in simple forms, what is/are the difference(s) between
>
> - scanf and sscanf and ssscanf
> - printf and sprintf
> - open and fopen[/color]


What does your C textbook say? Learning C from random questions on
usenet is a bad idea and no substitute for proper study. You are wasting
your time and ours.




Brian Rodenborn

[Nils O. Selåsdal]

Re: Difference between various functions

On Mon, 14 Jun 2004 04:47:13 -0700, SDZ wrote:
[color=blue]
> Could somebody explain in simple forms, what is/are the difference(s) between
>
> - scanf and sscanf and ssscanf
> - printf and sprintf
> - open and fopen
>
> Thanks in advance,
> SDZ[/color]
int scanf(const char *format, ...);
int sscanf(const char *str, const char *format, ...);
(never heard of ssscanf)
int printf(const char *format, ...);
int sprintf(char *str, const char *format, ...);

int open(const char *pathname, int flags);
int open(const char *pathname, int flags, mode_t mode);
FILE *fopen(const char *path, const char *mode);

You can easily see some docs for these in section 2 and 3
at e.g. http://netbsd.gw.com/cgi-bin/man-cgi

[Joona I Palaste]

Re: Difference between various functions

Nils O. Selåsdal <NOS@utel.no> scribbled the following:[color=blue]
> On Mon, 14 Jun 2004 04:47:13 -0700, SDZ wrote:[color=green]
>> Could somebody explain in simple forms, what is/are the difference(s) between
>> - open and fopen[/color][/color]
[color=blue]
> int open(const char *pathname, int flags);
> int open(const char *pathname, int flags, mode_t mode);
> FILE *fopen(const char *path, const char *mode);[/color]

Wait, wait. Two distinct functions with the same name aren't possible in
ISO-compliant C, even if they use different parameters. Does the POSIX
standard actually require the compiler to use non-standard extensions?

--
/-- Joona Palaste (palaste@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Normal is what everyone else is, and you're not."
- Dr. Tolian Soran

[Dragan Cvetkovic]

Re: Difference between various functions

Joona I Palaste <palaste@cc.hel sinki.fi> writes:
[color=blue]
> Nils O. Selåsdal <NOS@utel.no> scribbled the following:[color=green]
>> On Mon, 14 Jun 2004 04:47:13 -0700, SDZ wrote:[color=darkred]
>>> Could somebody explain in simple forms, what is/are the difference(s) between
>>> - open and fopen[/color][/color]
>[color=green]
>> int open(const char *pathname, int flags);
>> int open(const char *pathname, int flags, mode_t mode);[/color]
>
> Wait, wait. Two distinct functions with the same name aren't possible in
> ISO-compliant C, even if they use different parameters. Does the POSIX
> standard actually require the compiler to use non-standard extensions?[/color]

Well, the actuall prototype should be

int open(const char *, int, ...);

or, as commonly used in documentation

int open(const char *path, int oflag, /* mode_t mode */);

and that C handles quite well using <stdarg.h> type of functions.

The same way you handle fprintf(...) type of functions.

Bye, Dragan

--
Dragan Cvetkovic,

To be or not to be is true. G. Boole No it isn't. L. E. J. Brouwer

!!! Sender/From address is bogus. Use reply-to one !!!

[Eric Sosman]

Re: Difference between various functions

Joona I Palaste wrote:[color=blue]
> Nils O. Selåsdal <NOS@utel.no> scribbled the following:
> [color=green]
>>On Mon, 14 Jun 2004 04:47:13 -0700, SDZ wrote:
>>[color=darkred]
>>>Could somebody explain in simple forms, what is/are the difference(s) between
>>>- open and fopen[/color][/color]
>
> [color=green]
>>int open(const char *pathname, int flags);
>>int open(const char *pathname, int flags, mode_t mode);
>>FILE *fopen(const char *path, const char *mode);[/color]
>
>
> Wait, wait. Two distinct functions with the same name aren't possible in
> ISO-compliant C, even if they use different parameters. Does the POSIX
> standard actually require the compiler to use non-standard extensions?[/color]

<OT> I think

int open(const char *path, int flags, ...);

is acceptable. </OT>

--
Eric.Sosman@sun .com

[Goran Larsson]

Re: Difference between various functions

In article <cal2es$cr9$1@o ravannahka.hels inki.fi>,
Joona I Palaste <palaste@cc.hel sinki.fi> wrote:
[color=blue]
> Nils O. Selåsdal <NOS@utel.no> scribbled the following:[color=green]
> > int open(const char *pathname, int flags);
> > int open(const char *pathname, int flags, mode_t mode);[/color][/color]
[color=blue]
> Wait, wait. Two distinct functions with the same name aren't possible in
> ISO-compliant C, even if they use different parameters.[/color]

It is possible if it can be implemented as a function with a variable
argument list, like this:

| #if defined(__STDC_ _)
|
| extern int fcntl(int, int, ...);
| extern int open(const char *, int, ...);

The open() function only needs to look at the third argument (mode) if
a certain bit (O_CREAT) is set in the second argument (flags).
[color=blue]
> Does the POSIX
> standard actually require the compiler to use non-standard extensions?[/color]

No non-standard extensions are required.

--
Göran Larsson http://www.mitt-eget.com/

[Ben Pfaff]

Re: Difference between various functions

Joona I Palaste <palaste@cc.hel sinki.fi> writes:
[color=blue]
> Nils O. Selåsdal <NOS@utel.no> scribbled the following:[color=green]
>> int open(const char *pathname, int flags);
>> int open(const char *pathname, int flags, mode_t mode);[/color]
>
> Wait, wait. Two distinct functions with the same name aren't possible in
> ISO-compliant C, even if they use different parameters. Does the POSIX
> standard actually require the compiler to use non-standard extensions?[/color]

No. Typically open() is actually prototyped as
int open(const char *, int, ...);
--
"In My Egotistical Opinion, most people's C programs should be indented six
feet downward and covered with dirt." -- Blair P. Houghton

[Barry Margolin]

Re: Difference between various functions

In article <cal2es$cr9$1@o ravannahka.hels inki.fi>,
Joona I Palaste <palaste@cc.hel sinki.fi> wrote:
[color=blue]
> Nils O. Selåsdal <NOS@utel.no> scribbled the following:[color=green]
> > On Mon, 14 Jun 2004 04:47:13 -0700, SDZ wrote:[color=darkred]
> >> Could somebody explain in simple forms, what is/are the difference(s)
> >> between
> >> - open and fopen[/color][/color]
>[color=green]
> > int open(const char *pathname, int flags);
> > int open(const char *pathname, int flags, mode_t mode);
> > FILE *fopen(const char *path, const char *mode);[/color]
>
> Wait, wait. Two distinct functions with the same name aren't possible in
> ISO-compliant C, even if they use different parameters. Does the POSIX
> standard actually require the compiler to use non-standard extensions?[/color]

No, they require support for varargs functions, which is standard. The
actual prototype is:

int open(const char *pathname, int flags, ...);

But the only valid ways to call it correspond to the two prototypes that
Nils showed.

--
Barry Margolin, barmar@alum.mit .edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***

[Joona I Palaste]

Re: Difference between various functions

Goran Larsson <hoh@invalid.in valid> scribbled the following
on comp.lang.c:[color=blue]
> In article <cal2es$cr9$1@o ravannahka.hels inki.fi>,
> Joona I Palaste <palaste@cc.hel sinki.fi> wrote:[/color]
[color=blue][color=green]
>> Nils O. Selåsdal <NOS@utel.no> scribbled the following:[color=darkred]
>> > int open(const char *pathname, int flags);
>> > int open(const char *pathname, int flags, mode_t mode);[/color][/color][/color]
[color=blue][color=green]
>> Wait, wait. Two distinct functions with the same name aren't possible in
>> ISO-compliant C, even if they use different parameters.[/color][/color]
[color=blue]
> It is possible if it can be implemented as a function with a variable
> argument list, like this:[/color]
[color=blue]
> | #if defined(__STDC_ _)
> |
> | extern int fcntl(int, int, ...);
> | extern int open(const char *, int, ...);[/color]
[color=blue]
> The open() function only needs to look at the third argument (mode) if
> a certain bit (O_CREAT) is set in the second argument (flags).[/color]
[color=blue][color=green]
>> Does the POSIX
>> standard actually require the compiler to use non-standard extensions?[/color][/color]
[color=blue]
> No non-standard extensions are required.[/color]

D'oh. I should have paid more attention to the parameter lists. Even
ISO standard C functions (printf, fprint, ...) work that way. Thanks to
all who replied.
One further question: Since AFAIK ISO standard C provides no way to
explicitly check the length of the varargs list, how does open() know
whether the "mode" argument was supplied or not? Or does it even need
to?

--
/-- Joona Palaste (palaste@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"I said 'play as you've never played before', not 'play as IF you've never
played before'!"
- Andy Capp

[Rich Teer]

Re: Difference between various functions

On Mon, 14 Jun 2004, Joona I Palaste wrote:
[color=blue]
> One further question: Since AFAIK ISO standard C provides no way to
> explicitly check the length of the varargs list, how does open() know
> whether the "mode" argument was supplied or not? Or does it even need
> to?[/color]

It doesn't need to know. The writers of the function quite
reasonably assume that if O_CREAT was specified, then the 3rd
argument was also passed. If it wasn't passed, whatever junk
is on the stack at that location will be used instead.

--
Rich Teer, SCNA, SCSA

President,
Rite Online Inc.

Voice: +1 (250) 979-1638
URL: http://www.rite-online.net

[Joona I Palaste]

Re: Difference between various functions

Rich Teer <rich.teer@ri te-group.com> scribbled the following
on comp.lang.c:[color=blue]
> On Mon, 14 Jun 2004, Joona I Palaste wrote:[color=green]
>> One further question: Since AFAIK ISO standard C provides no way to
>> explicitly check the length of the varargs list, how does open() know
>> whether the "mode" argument was supplied or not? Or does it even need
>> to?[/color][/color]
[color=blue]
> It doesn't need to know. The writers of the function quite
> reasonably assume that if O_CREAT was specified, then the 3rd
> argument was also passed. If it wasn't passed, whatever junk
> is on the stack at that location will be used instead.[/color]

All righty, thanks. I note that this behaviour is dependent on the
POSIX standard and the ISO C standard alone does not suffice to
guarantee it.

--
/-- Joona Palaste (palaste@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Nothing lasts forever - so why not destroy it now?"
- Quake

[Goran Larsson]

Re: Difference between various functions

In article <Pine.SOL.4.58. 0406141512250.1 2483@zaphod.rit e-online.net>,
Rich Teer <rich.teer@ri te-group.com> wrote:
[color=blue]
> If it wasn't passed, whatever junk
> is on the stack at that location will be used instead.[/color]

| If it wasn't passed, whatever junk
| is in the implementation specific location[*] used to pass arguments
| will be used instead.
|
|[*] location includes memory, registers, disks, punched cards,
| mercury delay lines, ...

Writing about "the stack" in comp.lang.c is not recommended. :-/

--
Göran Larsson http://www.mitt-eget.com/