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Top Forums Programming sizeof an array of structure without using 'sizeof' operator Post 302302724 by shamrock on Tuesday 31st of March 2009 07:37:33 PM
Old 03-31-2009
The pragma directive lets you alter the packing of structures but has no affect on ordinary variables. Also it is non-portable and should not be used in code that will be deployed to multiple OSes AIX HPUX Solaris Linux. Output below is from an AIX machine...
Code:
#include <stdio.h>

#pragma pack(1)

int main(void)
{
    char beg;
    struct ptr
    {
        int a;
        char b;
        int *p;
    } abc;
    char end;

    printf("Using sizeof operator = %u\n", sizeof(abc));

    printf("beg address = %lu\n", (unsigned long) &beg);
    printf("end address = %lu\n", (unsigned long) &end);
    printf("first element address = %lu\n", (unsigned long) &abc.a);
    printf("last element address = %lu\n", (unsigned long) &abc.p);
    printf("size of structure = %lu\n", (unsigned long) &end - (unsigned long) &abc.a);
}

Output...
Code:
using sizeof operator = 9
beg address = 104399808
end address = 104399821
first element address = 104399812
last element address = 104399817
size of structure = 9


Last edited by shamrock; 03-31-2009 at 08:45 PM..
 

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std::mask_array< _Tp >(3)				     Library Functions Manual					 std::mask_array< _Tp >(3)

NAME
std::mask_array< _Tp > - SYNOPSIS
Public Types typedef _Tp value_type Public Member Functions mask_array (const mask_array &) void operator%= (const valarray< _Tp > &) const template<class _Dom > void operator%= (const _Expr< _Dom, _Tp > &) const void operator&= (const valarray< _Tp > &) const template<class _Dom > void operator&= (const _Expr< _Dom, _Tp > &) const void operator*= (const valarray< _Tp > &) const template<class _Dom > void operator*= (const _Expr< _Dom, _Tp > &) const void operator+= (const valarray< _Tp > &) const template<class _Dom > void operator+= (const _Expr< _Dom, _Tp > &) const void operator-= (const valarray< _Tp > &) const template<class _Dom > void operator-= (const _Expr< _Dom, _Tp > &) const void operator/= (const valarray< _Tp > &) const template<class _Dom > void operator/= (const _Expr< _Dom, _Tp > &) const void operator<<= (const valarray< _Tp > &) const template<class _Dom > void operator<<= (const _Expr< _Dom, _Tp > &) const mask_array & operator= (const mask_array &) void operator= (const valarray< _Tp > &) const void operator= (const _Tp &) const template<class _Dom > void operator= (const _Expr< _Dom, _Tp > &) const template<class _Ex > void operator= (const _Expr< _Ex, _Tp > &__e) const void operator>>= (const valarray< _Tp > &) const template<class _Dom > void operator>>= (const _Expr< _Dom, _Tp > &) const void operator^= (const valarray< _Tp > &) const template<class _Dom > void operator^= (const _Expr< _Dom, _Tp > &) const void operator|= (const valarray< _Tp > &) const template<class _Dom > void operator|= (const _Expr< _Dom, _Tp > &) const Friends class valarray< _Tp > Detailed Description template<class _Tp>class std::mask_array< _Tp > Reference to selected subset of an array. A mask_array is a reference to the actual elements of an array specified by a bitmask in the form of an array of bool. The way to get a mask_array is to call operator[](valarray<bool>) on a valarray. The returned mask_array then permits carrying operations out on the referenced subset of elements in the original valarray. For example, if a mask_array is obtained using the array (false, true, false, true) as an argument, the mask array has two elements referring to array[1] and array[3] in the underlying array. Parameters: Tp Element type. Definition at line 83 of file valarray. Author Generated automatically by Doxygen for libstdc++ from the source code. libstdc++ Tue Jun 10 2014 std::mask_array< _Tp >(3)
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