.\" Automatically generated by Pandoc 2.2.1
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.TH "POBJ_LAYOUT_BEGIN" "3" "2019-02-19" "PMDK - pmemobj API version 2.3" "PMDK Programmer's Manual"
.hy
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.SH NAME
.PP
\f[B]POBJ_LAYOUT_BEGIN\f[](), \f[B]POBJ_LAYOUT_TOID\f[](),
\f[B]POBJ_LAYOUT_ROOT\f[](), \f[B]POBJ_LAYOUT_NAME\f[](),
\f[B]POBJ_LAYOUT_END\f[](), \f[B]POBJ_LAYOUT_TYPES_NUM\f[]() \-
persistent memory transactional object store layout
.SH SYNOPSIS
.IP
.nf
\f[C]
#include\ <libpmemobj.h>

POBJ_LAYOUT_BEGIN(layout)
POBJ_LAYOUT_TOID(layout,\ TYPE)
POBJ_LAYOUT_ROOT(layout,\ ROOT_TYPE)
POBJ_LAYOUT_NAME(layout)
POBJ_LAYOUT_END(layout)
POBJ_LAYOUT_TYPES_NUM(layout)
\f[]
.fi
.SH DESCRIPTION
.PP
\f[B]libpmemobj\f[](7) defines a set of macros for convenient
declaration of a pool's layout.
The layout declaration consists of declarations of a number of used
types.
The declared types will be assigned consecutive type numbers.
Declared types may be used in conjunction with type safety macros (see
\f[B]TOID_DECLARE\f[](3)).
Once created, the layout declaration must not be changed unless any new
types are added at the end of the existing layout declaration.
Modifying any existing declaration may lead to changes in the type
numbers of declared types, which in consequence may cause data
corruption.
.PP
The \f[B]POBJ_LAYOUT_BEGIN\f[]() macro indicates a begin of declaration
of layout.
The \f[I]LAYOUT\f[] argument is a name of layout.
This argument must be passed to all macros related to the declaration of
layout.
.PP
The \f[B]POBJ_LAYOUT_TOID\f[]() macro declares a typed \f[I]OID\f[] for
type passed as \f[I]TYPE\f[] argument inside the declaration of layout.
All types declared using this macro are assigned with consecutive type
numbers.
This macro must be used between the \f[B]POBJ_LAYOUT_BEGIN\f[]() and
\f[B]POBJ_LAYOUT_END\f[]() macros, with the same name passed as
\f[I]LAYOUT\f[] argument.
.PP
The \f[B]POBJ_LAYOUT_ROOT\f[]() macro declares a typed \f[I]OID\f[] for
type passed as \f[I]ROOT_TYPE\f[] argument inside the declaration of
layout.
The typed \f[I]OID\f[] will be assigned with type number for root object
\f[B]POBJ_ROOT_TYPE_NUM\f[].
.PP
The \f[B]POBJ_LAYOUT_END\f[]() macro ends the declaration of layout.
.PP
The \f[B]POBJ_LAYOUT_NAME\f[]() macro returns the name of layout as a
null\-terminated string.
.PP
The \f[B]POBJ_LAYOUT_TYPES_NUM\f[]() macro returns number of types
declared using the \f[B]POBJ_LAYOUT_TOID\f[]() macro within the layout
declaration.
.SH EXAMPLE
.PP
This is an example of layout declaration:
.IP
.nf
\f[C]
POBJ_LAYOUT_BEGIN(mylayout);
POBJ_LAYOUT_ROOT(mylayout,\ struct\ root);
POBJ_LAYOUT_TOID(mylayout,\ struct\ node);
POBJ_LAYOUT_TOID(mylayout,\ struct\ foo);
POBJ_LAYOUT_END(mylayout);

struct\ root
{
\ \ \ \ TOID(struct\ node)\ node;
};

struct\ node
{
\ \ \ \ TOID(struct\ node)\ next;
\ \ \ \ TOID(struct\ foo)\ foo;
};
\f[]
.fi
.PP
The name of layout and the number of declared types can be retrieved
using the following code:
.IP
.nf
\f[C]
const\ char\ *layout_name\ =\ POBJ_LAYOUT_NAME(mylayout);
int\ num_of_types\ =\ POBJ_LAYOUT_TYPES_NUM(mylayout);
\f[]
.fi
.SH SEE ALSO
.PP
\f[B]TOID_DECLARE\f[](3), \f[B]libpmemobj\f[](7) and
\f[B]<http://pmem.io>\f[]