07-21-2010
main(), and functions in general, aren't sensible things to take a sizeof of. The compiler can't possibly know the code size yet. It's forbidden entirely in C++.
It doesn't make much sense to sizeof(void) either. void is a special variable type that can only be declared as a pointer and can't be dereferenced without typecasting. That it has a sizeof() at all is probably just to make pointer arithmetic simpler.
As for what a 'void *' type is incremented to, you can test that easily by printf("%p", pointer); It is incrememented as one byte, as you'd expect for a type with a sizeof(1). Makes sense. You don't know the size of its elements, if any, so assume the lowest common denominator.
As for why sizeof(i++) doesn't increment it, an expression isn't a sensible thing to take a sizeof either. sizeof() isn't a function call or any sort of runtime operation, the compiler substitutes one literal value at compile time and is done with it. The compiler doesn't have to calculate the value of i++ to understand that i+1 is still an integer, and substitute the size of an integer. It's more akin to a typedef than anything, and you wouldn't expect an expression to work in a typedef. But since sizeof() gets interspersed inside procedual code it has to tolerate more garbage.
In summary don't take the sizeof of an expression, function, or void thing. Only variables, pointers, and types. You'll always get sane results on those.
Last edited by Corona688; 07-21-2010 at 06:49 AM..
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elf64_fsize
elf32_fsize(3ELF) ELF Library Functions elf32_fsize(3ELF)
NAME
elf32_fsize, elf64_fsize - return the size of an object file type
SYNOPSIS
cc [ flag ... ] file ... -lelf [ library ... ]
#include <libelf.h>
size_t elf32_fsize(Elf_Type type, size_t count, unsigned ver);
size_t elf64_fsize(Elf_Type type, size_t count, unsigned ver);
DESCRIPTION
elf32_fsize() gives the size in bytes of the 32-bit file representation of count data objects with the given type. The library uses version
ver to calculate the size. See elf(3ELF) and elf_version(3ELF).
Constant values are available for the sizes of fundamental types:
Elf_Type File Size Memory Size
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ELF_T_BYTE 1 sizeof(unsigned char)
ELF_T_HALF ELF32_FSZ_HALF sizeof(Elf32_Half)
ELT_T_OFF ELF32_FSZ_OFF sizeof(Elf32_Off)
ELF_T_SWORD ELF32_FSZ_SWORD sizeof(Elf32_Sword)
ELF_T_WORD ELF32_FSZ_WORD sizeof(Elf32_Word)
elf32_fsize() returns 0 if the value of type or ver is unknown. See elf32_xlatetof(3ELF) for a list of the type values.
For the 64-bit class, replace 32 with 64 as appropriate.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Stable |
+-----------------------------+-----------------------------+
|MT-Level |MT-Safe |
+-----------------------------+-----------------------------+
SEE ALSO
elf(3ELF), elf32_xlatetof(3ELF), elf_version(3ELF), libelf(3LIB), attributes(5)
SunOS 5.10 11 Jul 2001 elf32_fsize(3ELF)