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Full Discussion: Function Returning Pointer
Top Forums Programming Function Returning Pointer Post 302507087 by Corona688 on Tuesday 22nd of March 2011 05:55:53 PM
Old 03-22-2011
Quote:
Originally Posted by majid.merkava
How about allocating memory with alloca function? because it allocates memory from stack frame.
alloca memory's main advantage, and main problem, is that it's fairy gold -- it vanishes. When your function returns, anything it's allocated with alloca becomes invalid (and potentially overwritten with trash). This means you don't have to free it yourself -- but you can't return it, either. You can pass it into a function, but can't pass it out of the function that allocated it.

alloca is fairly portable in one sense -- its convenience and (in some cases) performance advantage are tempting enough that you'll find it almost anywhere an implementation of it's even possible. But it's not actually defined by standard, and not actually possible everywhere. The long-standing flamewar over it is whether it should be considered a de-facto standard. Pros are it's simplicity and performance advantages. Its cons are potential bugs from implementations that don't do what you expect, limited stack memory, potential nonexistence if you port your code anywhere, and it not doing what you'd expect if you're used to malloc().

I think the best practice for returning a pointer is to take a pointer in the first place. Just use the memory you were given, then give it back. Where the memory came from and why becomes someone else's problem Smilie

Last edited by Corona688; 03-22-2011 at 07:10 PM..
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DWARF_GET_FUNCS(3)					   BSD Library Functions Manual 					DWARF_GET_FUNCS(3)

NAME
dwarf_get_funcs, dwarf_func_cu_offset, dwarf_func_die_offset, dwarf_func_name_offsets, dwarf_funcname -- retrieve information about static functions LIBRARY
DWARF Access Library (libdwarf, -ldwarf) SYNOPSIS
#include <libdwarf.h> int dwarf_get_funcs(Dwarf_Debug dbg, Dwarf_Func **funcs, Dwarf_Signed *nfuncs, Dwarf_Error *err); int dwarf_func_cu_offset(Dwarf_Func func, Dwarf_Off *cu_offset, Dwarf_Error *err); int dwarf_func_die_offset(Dwarf_Func func, Dwarf_Off *die_offset, Dwarf_Error *err); int dwarf_func_name_offsets(Dwarf_Func func, char **name, Dwarf_Off *die_offset, Dwarf_Off *cu_die_offset, Dwarf_Error *err); int dwarf_funcname(Dwarf_Func func, char **name, Dwarf_Error *err); DESCRIPTION
These functions retrieve information about static functions from the lookup tables in the (SGI-specific) ``.debug_funcnames'' section. Information about these functions is returned using opaque descriptors of type Dwarf_Func. Applications need to use the functions described below to retrieve the name and offset information contained in these descriptors. Function dwarf_get_funcs() retrieves descriptors for all the static functions associated with the DWARF debug context specified by argument dbg. The argument funcs should point to a location that will be set to a pointer to an array of Dwarf_Func descriptors. The argument nfuncs should point to a location that will be set to the number of descriptors returned. Function dwarf_func_cu_offset() returns the offset, relative to the ``.debug_info'' section, of the compilation unit that contains the debug- ging information entry associated with the argument func. Argument cu_offset should point to a location that will hold the returned offset. Function dwarf_func_die_offset() retrieves the offset, relative to the ``.debug_info'' section, of the debugging information entry associated with the argument func, and stores it into the location pointed to by the argument die_offset. Function dwarf_func_name_offsets() retrieves the name and offsets for the debugging information entry for argument func. Argument name should point to a location which will be set to a pointer to a NUL-terminated string containing the name of the associated debugging informa- tion entry. Argument die_offset should point to a location which will be set to the offset, relative to the ``.debug_info'' section, of the associated debugging information entry. Argument cu_die_offset should point to a location which will be set to the offset, relative to the ``.debug_info'' section, of the first debugging information entry in the compilation unit associated with argument func. Function dwarf_funcname() sets the location pointed to by argument name to a pointer to a NUL-terminated string holding the name of the debugging information entry associated with the argument func. Memory Management The memory area used for the array of Dwarf_Func descriptors returned in argument funcs by function dwarf_get_funcs() is owned by the DWARF Access Library (libdwarf, -ldwarf). Application code should not attempt to directly free this pointer. Portable code should instead use the function dwarf_funcs_dealloc(3) to indicate that the memory area may be freed. The memory area used for the string returned in the name argument to functions dwarf_func_name_offsets() and dwarf_funcname() is owned by the DWARF Access Library (libdwarf, -ldwarf). Portable code should indicate that the memory area can be freed using the dwarf_dealloc(3) func- tion. Error Returns If argument err is not NULL, these functions will use it to store error information, in case of an error. RETURN VALUES
On success, these functions returns DW_DLV_OK. In case of an error, they return DW_DLV_ERROR and set the argument err. ERRORS
These functions may fail with the following errors: [DW_DLE_ARGUMENT] One of the arguments cu_die_offset, cu_offset, dbg, die_offset, func, funcs, name, or nfuncs was NULL. [DW_DLE_NO_ENTRY] The DWARF debugging context referenced by argument dbg did not contain information about static functions. SEE ALSO
dwarf(3), dwarf_get_cu_die_offset_given_cu_header_offset(3), dwarf_funcs_dealloc(3) BSD
April 10, 2011 BSD
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