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Full Discussion: Doubts regarding sizeof() operator
Top Forums Programming Doubts regarding sizeof() operator Post 302438892 by Corona688 on Wednesday 21st of July 2010 05:43:02 AM
Old 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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LEARN ABOUT HPUX

elf_fsize

elf_fsize(3E)															     elf_fsize(3E)

NAME

       elf32_fsize,  elf64_fsize - return the size of an object file type for elf32 files, return the size of an object file type for elf64 files,
       respectively.

SYNOPSIS

       [flag... ] file...  [library] ...

DESCRIPTION

       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  cal-
       culate the size (see elf(3E) and elf_version(3E)).

       Constant values are available for the sizes of fundamental types.

						  Elf_Type	File Size	  Memory Size
						  ------------------------------------------------------
						  ELF_T_ADDR	ELF32_FSZ_ADDR	  sizeof(Elf32_Addr)
						  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)

       returns zero if the value of type or ver is unknown.  See elf_xlate(3E) for a list of the type values.

       gives  the size in bytes of the 64-bit file representation of count data objects with the given type.  The library uses version ver to cal-
       culate the size (see elf(3E) and elf_version(3E)).

       Constant values are available for the sizes of fundamental types.

						  Elf_Type	File Size	  Memory Size
						  ------------------------------------------------------
						  ELF_T_ADDR	ELF64_FSZ_ADDR	  sizeof(Elf64_Addr)
						  ELF_T_BYTE	1		  sizeof(unsigned char)
						  ELF_T_HALF	ELF64_FSZ_HALF	  sizeof(Elf64_Half)
						  ELT_T_OFF	ELF64_FSZ_OFF	  sizeof(Elf64_Off)
						  ELF_T_SWORD	ELF64_FSZ_SWORD   sizeof(Elf64_Sword)
						  ELF_T_WORD	ELF64_FSZ_WORD	  sizeof(Elf64_Word)

       returns zero if the value of type or ver is unknown.  See elf_xlate(3E) for a list of the type values.

SEE ALSO

       elf(3E), elf_version(3E), elf_xlate(3E).

																     elf_fsize(3E)
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