Category
Pragma equivalent
#pragma alloca
Purpose
Provides an inline definition of system function alloca when it is called from source code that does not include the alloca.h header.
The
function void* alloca(size_t size) dynamically
allocates memory, similarly to the standard library function malloc.
The compiler automatically substitutes calls to the system alloca function
with an inline built-in function __alloca in any
of the following cases:
- You include the header file alloca.h
- You compile with -Dalloca=__alloca
- You directly call the built-in function using the form __alloca
Syntax
Option syntax >>-+- -q--alloca-+--------------------------------------------->< '- -ma--------'
Defaults
Not applicable.
Usage
If you do not use any of the above-mentioned methods to ensure that calls to alloca are replaced with __alloca, alloca is treated as a user-defined identifier rather than as a built-in function.
Once specified, #pragma alloca applies to the rest of the file and cannot be disabled. If a source file contains any functions that you want compiled without #pragma alloca, place these functions in a different file.
You may want to consider using a C99 variable length array in place of alloca.
Predefined macros
None.
Examples
To compile myprogram.c so that calls to the function alloca are treated as inline, enter:
xlc myprogram.c -qalloca