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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function1 ()
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;;
*)
;;
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main()
{ (1 Reply)
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Hi,
I am having script which contains many functions. Need to print each function name at the starting of the function. Like below,
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commands....
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I've tried like below,
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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()
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if
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Discussion started by: meister29
4 Replies
LEARN ABOUT OSX
alloca
ALLOCA(3) BSD Library Functions Manual ALLOCA(3)NAME
alloca -- memory allocator
SYNOPSIS
#include <alloca.h>
or
#include <stdlib.h>
void *
alloca(size_t size);
DESCRIPTION
The alloca() macro allocates size bytes of space in the stack frame of the caller. This temporary space is automatically freed on return.
RETURN VALUES
alloca() returns a pointer to the beginning of the allocated space.
SEE ALSO brk(2), calloc(3), getpagesize(3), malloc(3), realloc(3)HISTORY
alloca() appeared in Version 32V AT&T UNIX.
BUGS
alloca() is machine and compiler dependent; its use is discouraged.
alloca() is slightly unsafe because it cannot ensure that the pointer returned points to a valid and usable block of memory. The allocation
made may exceed the bounds of the stack, or even go further into other objects in memory, and alloca() cannot determine such an error. Avoid
alloca() with large unbounded allocations.
The use of C99 variable-length arrays and alloca() in the same function will cause the lifetime of alloca's storage to be limited to the
block containing the alloca()
BSD September 5, 2006 BSD