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Full Discussion: help with data type sizes
Top Forums Programming help with data type sizes Post 302488046 by DGPickett on Friday 14th of January 2011 05:05:13 PM
Old 01-14-2011
Well, & is the address, and it goes up one for every char and usually 4 for every int. Addresses are guaranteed to be subtractable even if they are in odd formats internally. Also, adding integers is the same as offsetting an array, so for array "char c[] = "Hello" ;", c + 5 = &(c[5]) points c[5] = *(c+5) to the null of the "" string after the 'o' of hello.

For int arrays, adding one moves it 4 in char terms, but if you subtract int addresses, you get a result / 4 unless you cast them as (char*) first. So, for "int i[8];", &(i[5]) - &(i[2]) = 3, which turns out to be more useful than 12 unless you are doing i/o or malloc(), which are byte char operations.

If you are doing an array of struct, the struct size is multiplied for you into any increment or offset. You can discover the real size with sizeof() or by casting addresses of two adjacent struct to (char*) and subtracting, a popular interview question some places.
Last edited by DGPickett; 01-14-2011 at 06:12 PM..
 

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LEARN ABOUT OPENSOLARIS

m_getvalues_layout

m_getvalues_layout(3LAYOUT)				 Layout Service Library Functions			       m_getvalues_layout(3LAYOUT)

NAME

       m_getvalues_layout - query layout values of a LayoutObject

SYNOPSIS

       cc [ flag... ] file... -llayout [ library... ]
       #include <sys/layout.h>

       int m_getvalues_layout(const LayoutObject
	    layout_object, LayoutValues values, int *index_returned);

DESCRIPTION

       The m_getvalues_layout() function queries the current setting of layout values within a LayoutObject.

       The layout_object argument specifies a LayoutObject returned by the m_create_layout(3LAYOUT) function.

       The  values  argument  specifies  the  list of layout values that are to be queried. Each value element of a LayoutValueRec must point to a
       location where the layout value is stored. That is, if the layout value is of type T, the argument must be  of  type  T*.  The  values  are
       queried from the LayoutObject and represent its current state.

       It  is  the user's responsibility to manage the space allocation for the layout values queried. If the layout value name has QueryValueSize
       OR-ed to it, instead of the value of the layout value, only its size is returned. The caller can use this option to determine the amount of
       memory needed to be allocated for the layout values queried.

RETURN VALUES

       Upon successful completion, the m_getvalues_layout() function returns 0. If any value cannot be queried, the index of the value causing the
       error is returned in index_returned, -1 is returned and errno is set to indicate the error.

ERRORS

       The m_getvalues_layout() function may fail if:

       EINVAL	 The layout value specified by index_returned is unknown, its value is invalid, or the layout_object argument is invalid.  In  the
		 case of an invalid layout_object argument, the value returned in index_returned is -1.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       m_create_layout(3LAYOUT), attributes(5), standards(5)

SunOS 5.11							    7 Aug 2006					       m_getvalues_layout(3LAYOUT)
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