sizeof(object) in C++ Post: 302461858

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Top Forums Programming sizeof(object) in C++ Post 302461858 by ramkrix on Tuesday 12th of October 2010 02:49:03 PM

10-12-2010

Registered User

sizeof(object) in C++

Hi,

I have defined the class and call the sizeof(object to class) to get the size.

Code:

# include <iostream>
# include <iomanip>

using namespace std;
class sample
{
	private:
		int i;
		float j;
		char k;

	public:
		sample()
		{
		}
		
		sample(int a, float b, char c)
		{
			i=a;
			j=b;
			k=c;
		}

		void showdata()
		{
			cout<<"sizeof i="<<sizeof(i)<<endl;
			cout<<"sizeof j="<<sizeof(j)<<endl;
			cout<<"sizeof k="<<sizeof(k)<<endl;
			cout<<"i,j,k= "<<i<<"\t"<<j<<"\t"<<k<<endl;
		}
};

int main()
{
	sample q(3,4.5f,'Q'), w(3,5.67f,'W');
	q.showdata();
	cout<<"sizeof q is "<<sizeof(q)<<endl;
	cout<<"sizeof w is "<<sizeof(w)<<endl;
	return 0;
}

I expect the output of size of q and size of w to be "9" - since it is int+float+char(4+4+1)
However it returns 12. Can anybody explain why is it so??

Output as follows:

Code:

ganesh@ubuntu:~/my_programs/cpp/letuscpp$ g++ p22.cpp
ganesh@ubuntu:~/my_programs/cpp/letuscpp$ ./a.out
sizeof i=4
sizeof j=4
sizeof k=1
i,j,k= 3	4.5	Q
sizeof q is 12
sizeof w is 12

Thanks,
Ramkrix

Last edited by radoulov; 10-12-2010 at 03:55 PM.. Reason: Fixed code tags.

ramkrix

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LEARN ABOUT OPENDARWIN

elf32_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
	      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)

       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)

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