alloca(3) -- Linux man page
NAMEalloca - memory allocator
DESCRIPTIONThe 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 VALUEThe alloca function returns a pointer to the beginning of the allocated space. If the allocation causes stack overflow, program behaviour is undefined.
CONFORMING TOThere 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 VERSIONNormally, 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)
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.
BUGSThe 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 ALSObrk(2), pagesize(2), calloc(3), malloc(3), realloc(3)