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
37  8546  sh*********@yah oo.com (Shri) wrote in
news:8a******** *************** ***@posting.goo gle.com: 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 ...
Does strcat() help? If you need fancier concatenation, sprintf() might be
an option.
--
- Mark ->
--
Shri wrote: 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 ...
I *think* that what you are asking for is strcpy(), strcat(), etc.
You might also want to use strdup(), which is not specified in the
C standard but is available in every modern Unix system's C library.
And of course in the Unix (POSIX) system C library is also a family
of exec() functions. Learn to use "man -k", and also study a good
Unix programming text such as Kernighan & Pike.
It should also be noted that you shouldn't be writing programs that
run with elevated privilege (set-UID, daemon) without knowing a lot
more about security loopholes than you seem to be aware of.
"Douglas A. Gwyn" <DA****@null.ne t> writes: I *think* that what you are asking for is strcpy(), strcat(), etc.
You might also want to use strdup(), which is not specified in the
C standard but is available in every modern Unix system's C library.
And of course in the Unix (POSIX) system C library is also a family
of exec() functions. Learn to use "man -k", and also study a good
Unix programming text such as Kernighan & Pike.
It should also be noted that you shouldn't be writing programs that
run with elevated privilege (set-UID, daemon) without knowing a lot
more about security loopholes than you seem to be aware of.
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.
-SEan
Sean 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.
Richard
Sean Burke 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.
If you think that helps very much with security
then you're much mistaken. Presumably the idea is
to prevent buffer overflows, but that can also be
done in many other ways, many of them involving
only the standard C library functions. And anyway
neither an unchecked failure to fill a buffer nor
an unchecked truncation of the contents of a buffer
is very good from the standpoint of security. It's
a big subject, and as usual the attempt to automate
correct programming just changes the symptoms of a
problem without curing the disease.
Sean Burke <fo****@mystery .org> writes: "Douglas A. Gwyn" <DA****@null.ne t> writes:
I *think* that what you are asking for is strcpy(), strcat(), etc.
You might also want to use strdup(), which is not specified in the
C standard but is available in every modern Unix system's C library.
And of course in the Unix (POSIX) system C library is also a family
of exec() functions. Learn to use "man -k", and also study a good
Unix programming text such as Kernighan & Pike.
It should also be noted that you shouldn't be writing programs that
run with elevated privilege (set-UID, daemon) without knowing a lot
more about security loopholes than you seem to be aware of.
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.
I can't find those anywhere on my system, only strncpy and strncat.
The latter are defined by ISO C.
--
Måns Rullgård mr*@kth.se
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> writes Sean 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.
For a pathological case given, strlcpy is slightly slower than strcpy
and much faster than strncpy because strncpy pads with nul bytes.
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
Have the functions been submitted for C standardisation ?
--
Walter Briscoe
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.
Richard
Sean Burke <fo****@mystery .org> wrote in message news:<x7******* *****@bolo.xena dyne.com>... "Douglas A. Gwyn" <DA****@null.ne t> writes:
I *think* that what you are asking for is strcpy(), strcat(), etc.
You might also want to use strdup(), which is not specified in the
C standard but is available in every modern Unix system's C library.
And of course in the Unix (POSIX) system C library is also a family
of exec() functions. Learn to use "man -k", and also study a good
Unix programming text such as Kernighan & Pike.
It should also be noted that you shouldn't be writing programs that
run with elevated privilege (set-UID, daemon) without knowing a lot
more about security loopholes than you seem to be aware of.
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.
Have they?
They are not present in many frequently used operating systems.
They are not AFAIK part of the C standard, nor are they AFAIK part of
the POSIX standard. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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