Size of C/C++ data type from GNU GCC/g++ compiled ELF 64-bit LSB executable, AMD x86-64 vs. ELF 32-bit LSB executable, Intel 80386

[tom peng]

Hi Andrew,

Thanks for correcting my typo on "signed long int 4 8".

The problem I have here is about simulating a hardware model in C/C++. The
hardware model development was based on 32-bit CPU originally. We had
presumed "signed long int" as 32-bit/4 byte length -- as specified in C/C++
code "typedef signed long int int32".

It is apparent that this "int32" in 64-bit ELF executable is of length 8
bytes, not what we expect. It "might" cause the hw simulation inconsistency
when running in 64 vs. 32 ELF format.

I hope to get a generic picture about the size difference of C/C++ data type
and their modifiers in 32/64 ELF format compiled by GCC.

Are those 32-bit / 64-bit difference stipulated in C/C++ standard or ruled
by the GNU/GCC compiler?

Thank you very much,

Tom



Andrew Haley-5 wrote:
> 
> tom peng writes:
>  > 
>  > I posted this message on gcc/bug forum earlier. I repost the same
> contents
>  > here. I need experts to shed light on C/C++ data type size
> inconsistencies
>  > when running 64-bit and 32-bit ELF executables compiled by GNU/GCC
> g++/gcc
>  > 
>  > Following are results of C/C++ data type size from code " cout << "data
>  > type" << sizeof(data type) << endl " :
>  > 
>  >                      | 32-bit | 64-bit
>  > -------------------------------
>  > int                 |    4     |    4
>  > -------------------------------
>  > long int           |    4     |    8
>  > -------------------------------
>  > signed long int  |    4     |    4
> 
> No, that should be  4   8
> 
>  > -------------------------------
>  > ulong              |    4     |    8      (sys/types.h)
>  > -------------------------------
>  > long double      |    12   |    16
> 
> Seems OK otherwise.  What's your problem?
> 
> Andrew.
> 
> 

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