hi all,
i am writing a code in which i have a char buffer "cwdir[]"
which hold the current working directory by calling the function
getcwd(). later i change the directory to "/" as i have to make my
code Deamon. and later again i want to run some other executable
available at the path holded by the "cwdir[]" using the system()
system call. presently i concatenate program name (to be executed) to
the "cwdir[]" and use system(chdir)to run the program.
do we have any facility to automate this process as i need to run
many other programs also using the system() system call for ex as we
can use the ## symbol to cancatenate in macro ...
--shri
Nov 14 '05
37  8548 
In <x7************ @bolo.xenadyne. com> Sean Burke <fo****@mystery .org> writes: Since you mention security (e.g. buffer overflows),
it's worth adding that strcpy, strcat have long since
been deprecated in favor of strlcpy, strlcat.
On the contrary, any C program using these identifiers with external
linkage invokes undefined behaviour.
Whoever wanted to improve upon strcpy and friends should have had enough
clues to avoid identifiers belonging to the implementation name space.
lstrcpy() and lstrcat() would have been ideal names for this purpose.
Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de Da*****@cern.ch (Dan Pop) writes: In <x7************ @bolo.xenadyne. com> Sean Burke <fo****@mystery .org> writes:
Since you mention security (e.g. buffer overflows),
it's worth adding that strcpy, strcat have long since
been deprecated in favor of strlcpy, strlcat.
On the contrary, any C program using these identifiers with external
linkage invokes undefined behaviour.
Maybe Mr. Burke misspelled "strncpy" and "strncat", mentioned in
ISO/IEC 9899:1999 under 7.21.2.4 and 7.21.3.2 ? Their prototypes (in
<string.h>) are
char *strncpy(char * restrict, const char * restrict, size_t);
char *strncat(char * restrict, const char * restrict, size_t);
--
Maurizio Loreti http://www.pd.infn.it/~loreti/mlo.html
Dept. of Physics, Univ. of Padova, Italy ROT13: yb****@cq.vasa. vg
Maurizio Loreti <ml*@foobar.i t> writes: Da*****@cern.ch (Dan Pop) writes:
In <x7************ @bolo.xenadyne. com> Sean Burke
<fo****@mystery .org> writes:
>Since you mention security (e.g. buffer overflows),
>it's worth adding that strcpy, strcat have long since
>been deprecated in favor of strlcpy, strlcat.
On the contrary, any C program using these identifiers with external
linkage invokes undefined behaviour.
Maybe Mr. Burke misspelled "strncpy" and "strncat", mentioned in
ISO/IEC 9899:1999 under 7.21.2.4 and 7.21.3.2 ? Their prototypes (in
<string.h>) are
char *strncpy(char * restrict, const char * restrict, size_t);
char *strncat(char * restrict, const char * restrict, size_t);
Maybe he meant those, but the non-standard strl* variants are more
useful. The return values from the standard str* functions are
utterly useless, since you already knew the value. Returning the
number bytes copied is much more useful. BTW, str*cat should be used
sparingly. In most cases you have, or can easily get (cheaper than
scanning), a pointer to the end of the destination string.
--
Måns Rullgård mr*@kth.se
Maurizio Loreti <ml*@foobar.i t> writes: Da*****@cern.ch (Dan Pop) writes:
In <x7************ @bolo.xenadyne. com> Sean Burke <fo****@mystery .org> writes:
Since you mention security (e.g. buffer overflows),
it's worth adding that strcpy, strcat have long since
been deprecated in favor of strlcpy, strlcat.
On the contrary, any C program using these identifiers with external
linkage invokes undefined behaviour.
Maybe Mr. Burke misspelled "strncpy" and "strncat", mentioned in
ISO/IEC 9899:1999 under 7.21.2.4 and 7.21.3.2 ? Their prototypes (in
<string.h>) are
char *strncpy(char * restrict, const char * restrict, size_t);
char *strncat(char * restrict, const char * restrict, size_t);
No, I meant strlcpy/strlcat, and I find them to be better
than the strn* calls. I'm astonished to learn that they
aren't yet standardised.
-SEan rl*@hoekstra-uitgeverij.nl (Richard Bos) writes: Walter Briscoe <wb******@ponle .demon.co.uk> wrote:
In message <40************ ***@news.indivi dual.net> of Fri, 13 Feb 2004
08:06:19 in comp.std.c, Richard Bos <rl*@hoekstra-uitgeverij.nl> writesSean Burke <fo****@mystery .org> wrote:
> Since you mention security (e.g. buffer overflows),
> it's worth adding that strcpy, strcat have long since
> been deprecated in favor of strlcpy, strlcat.
Not in ISO C, they haven't. Maybe in POSIX.
Neither there!
(http://www.opengroup.org/onlinepubs/.../string.h.html)
They ARE documented at http://www.courtesan.com/todd/papers/strlcpy.html
My summary of that is
size_t strlcpy(char *dst, const char *src, size_t size);
Copy a string of up to size-1 bytes from src to dst. Return strlen(src).
size_t strlcat(char *dst, const char *src, size_t size);
Concatenate bytes from src to dst to form a string with strlen(dst) <
size. Return strlen(dst) /* before concatenation */ + strlen(src).
The functions allow buffer overflow elimination.
Nice, meaningless statement; so does strncat(), and so does using
strlen() and inserting a '\0' at the right place before using strcpy().
Have the functions been submitted for C standardisation ?
No. Might be a nice addition, but I wouldn't describe them as vital.
Mind you, I won't complain if they _are_ added to C20XX.
Don't tell me that snprintf, vsnprintf() are also nonstandard?
-SEan
Sean Burke wrote:
.... Don't tell me that snprintf, vsnprintf() are also nonstandard?
No: see sections 7.19.6.5 and 7.19.6.12.
In article <c0**********@s unnews.cern.ch> , Da*****@cern.ch (Dan Pop) writes: In <x7************ @bolo.xenadyne. com> Sean Burke <fo****@mystery .org> writes:
Since you mention security (e.g. buffer overflows),
it's worth adding that strcpy, strcat have long since
been deprecated in favor of strlcpy, strlcat.
On the contrary, any C program using these identifiers with external
linkage invokes undefined behaviour.
Whoever wanted to improve upon strcpy and friends should have had enough
clues to avoid identifiers belonging to the implementation name space.
Presumably in at least some cases they could be provided by the
implementation, and in such a case programs using them would not
invoke UB, correct? This could potentially raise some tricky
questions about what is and what is not part of the implementation, I
suppose.
That said, I agree with the general point. An implementor has reason
to use a reserved identifier for a new function (it won't break
existing conforming code), but no one else does. I suppose someone
could argue that Miller and de Raadt were implementors when they
invented strlcpy and strlcat and added them to OpenBSD, since AFAICT
they added them directly to the standard library there, but their
choice of identifiers means non-implementors have to rename their
functions when porting them to other implementations .
--
Michael Wojcik mi************@ microfocus.com
Pocket #9: A complete "artificial glen" with rocks, and artificial moon,
and forester's station. Excellent for achieving the effect of the
sublime without going out-of-doors. -- Joe Green
On Fri, 13 Feb 2004 10:19:47 +0000, Walter Briscoe wrote: They ARE documented at http://www.courtesan.com/todd/papers/strlcpy.html
My summary of that is
size_t strlcpy(char *dst, const char *src, size_t size); Copy a string of
up to size-1 bytes from src to dst. Return strlen(src).
size_t strlcat(char *dst, const char *src, size_t size); Concatenate bytes
from src to dst to form a string with strlen(dst) < size. Return
strlen(dst) /* before concatenation */ + strlen(src).
All the documentation, including the above, is laughable compared to
normal std. C text. Which is probably why there are a couple of different
implementations and the two major non OpenBSD implementations are
_documented_ to act differently than the OpenBSD versions do.
The functions allow buffer overflow elimination. For a pathological case
given, strlcpy is slightly slower than strcpy and much faster than strncpy
because strncpy pads with nul bytes.
IMO they are even more worthless than asprintf(), they are documented
to act differently on different platforms and (unlike asprintf() you can
still cause security issues due to truncation of data).
The authors added them to OpenBSD in 1996 and report their approval for a
future Solaris version in their undated paper. Source code is said to be
available at ftp://ftp.openbsd.org/pub/OpenBSD/src/lib/libc/string
The "undated" paper has references to papers published in 1998, and says:
"The strlcpy() and strlcat() functions first appeared in OpenBSD 2.4."
....which dates them between May 19, and December 1, 1998. People
_started_ to hear of them after the 1999 Usenix when the paper... http://www.usenix.org/events/usenix9...rt/millert.pdf
....was presented, which even then as way too late for C99 ... and I don't
remember hearing about them until 2000 (which was after the last std. was
released).
--
James Antill -- ja***@and.org
Need an efficient and powerful string library for C? http://www.and.org/vstr/
On Fri, 13 Feb 2004 17:12:51 +0000, Sean Burke wrote: No, I meant strlcpy/strlcat, and I find them to be better than the strn*
calls. I'm astonished to learn that they aren't yet standardised.
Not only are they not in std. C, they aren't available at all on any
of the major Linux variants. They also are/were implemented subtly
differently on Solaris.
You probably also want to read: http://www.and.org/vstr/security.html#alloc
--
James Antill -- ja***@and.org
Need an efficient and powerful string library for C? http://www.and.org/vstr/
James Antill <ja***********@ and.org> writes: Not only are they not in std. C, they aren't available at all on any
of the major Linux variants. They also are/were implemented subtly
differently on Solaris.
They weren't implemented subtly different on Solaris; our implementation
is a straightforward clone from the original OpenBSD version and behaves
exactly the same.
You may be confused with "snprintf() " where Solaris originally
implemented it differently for "n = 0"; UNIX98 standardized
snprintf that it should return a value <= 0 for n = 0 and we're
a bit of a stickler for standards.
UNIX03 fixes that, fortunately, so the Solaris release will
have an snprintf which allows you to call it as follows:
size_t len = snprintf(0, NULL, .....);
to compute the length needed (note that snprintf can return
"-1" and set errno to EILSEQ.
Casper
--
Expressed in this posting are my opinions. They are in no way related
to opinions held by my employer, Sun Microsystems.
Statements on Sun products included here are not gospel and may
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