I don't know of any platforms that don't support alloca apart from embedded OSes however as the manpages say it is system dependent. Personally I have never used alloca because it is really of no use when it cant be returned. Curious if you can come up with a scenario where it's use would be more befitting than malloc.
Any time you want a local buffer without predefining its size, for one thing. achenle also had a good point about it being threadsafe hence much faster than trying to synchronize malloc for multithreaded things.
It's interesting how each platform discourages the use of alloca because of how it might behave on some other unmentionable platform without confessing to being guilty themselves. This could stand some testing, I think. alloca's almost as old as UNIX itself, circa AT&T V32 1979, making me wonder how historical this complaint is and how relevant it actually remains.
---------- Post updated at 04:24 PM ---------- Previous update was at 03:57 PM ----------
I wonder if this fails on any of your machines. I'm trying to smash stack memory in the manner described by passing and assigning to large stack variables as well as deep recursion.
So far OSX on PPC, and Linux on x86-32, x86-64, and embedded-linux MIPS(with ulibc) do not accidentally overwrite memory returned by alloca.
Last edited by Corona688; 10-27-2009 at 12:33 PM..
Hi ,
I have three funcions f1, f2 and f3 .
f1 calls f2 and f2 calls f3 .
I have a global variable "period" which i want to pass to f3 .
Can i pass the variable directly in the definition of f3 ?
Pls help .
sars (4 Replies)
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function InsertFtg
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function1 ()
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function2()
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case $1 in
January)
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;;
*)
;;
}
main()
{ (1 Reply)
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Dear All.
I have a script, which process files one by one. In the script I have two functions.
one sftp files to different server
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My question is:
Will sftp function recognize files names , which are created in another... (1 Reply)
Hi,
I am having script which contains many functions. Need to print each function name at the starting of the function. Like below,
functionname()
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echo "functionname"
commands....
}
I've tried like below,
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nawk -v... (4 Replies)
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Hi All,
Good Day, seeking for your assistance on how to not perform my 2nd, 3rd,4th etc.. function if my 1st function is in else condition.
#Body
function1()
{
if
then
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else
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#if not exist in function1 my all other function will not proceed.... (4 Replies)
Discussion started by: meister29
4 Replies
LEARN ABOUT REDHAT
alloca
ALLOCA(3) Linux Programmer's Manual ALLOCA(3)NAME
alloca - memory allocator
SYNOPSIS
#include <alloca.h>
void *alloca(size_t size);
DESCRIPTION
The alloca function allocates size bytes of space in the stack frame of the caller. This temporary space is automatically freed when the
function that called alloca returns to its caller.
RETURN VALUE
The alloca function returns a pointer to the beginning of the allocated space. If the allocation causes stack overflow, program behaviour
is undefined.
CONFORMING TO
There is evidence that the alloca function appeared in 32v, pwb, pwb.2, 3bsd, and 4bsd. There is a man page for it in BSD 4.3. Linux uses
the GNU version. This function is not in POSIX or SUSv3.
NOTES ON THE GNU VERSION
Normally, gcc translates calls to alloca by inlined code. This is not done when either the -ansi or the -fno-builtin option is given. But
beware! By default the glibc version of <stdlib.h> includes <alloca.h> and that contains the line
# define alloca(size) __builtin_alloca (size)
with messy consequences if one has a private version of this function.
The fact that the code is inlined, means that it is impossible to take the address of this function, or to change its behaviour by linking
with a different library.
The inlined code often consists of a single instruction adjusting the stack pointer, and does not check for stack overflow. Thus, there is
no NULL error return.
BUGS
The alloca function is machine and compiler dependent. On many systems its implementation is buggy. Its use is discouraged.
On many systems alloca cannot be used inside the list of arguments of a function call, because the stack space reserved by alloca would
appear on the stack in the middle of the space for the function arguments.
SEE ALSO brk(2), pagesize(2), calloc(3), malloc(3), realloc(3)GNU 2002-07-17 ALLOCA(3)