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.Dd December 21, 2022
.Dt AG_VERSION 3
.Os Agar 1.7
.Sh NAME
.Nm AG_Version
.Nd agar data file versioning
.Sh SYNOPSIS
.Bd -literal
#include <agar/core.h>
.Ed
.Sh DESCRIPTION
The
.Nm
structure represents a version number for an
.Xr AG_Object 3
(or any other type of data).
It is defined as follows:
.Pp
.Bd -literal -offset indent
.\" SYNTAX(c)
typedef struct ag_version {
	Uint32 major;    /* Major version number */
	Uint32 minor;    /* Minor version number */
	Uint32 cid;	 /* Class ID */
	Uint32 unicode;  /* Icon (Unicode value) */
} AG_Version;
.Ed
.Pp
The
.Va major
version number is incremented whenever a change introduces any type of
binary incompatibility with previous versions of the data file.
.Pp
The
.Va minor
number is incremented when a new feature is introduced which does not break
binary compatibility with previous versions.
A typical deserialization routine may test the minor number to determine
the presence of new features (which do not break binary compatibility).
.Pp
The
.Va cid
field is a 32-bit numerical class ID (or 0).
.Pp
The
.Va unicode
field is an optional Unicode character value (or 0).
.Sh VERSIONING
.nr nS 1
.Ft "int"
.Fn AG_ReadVersion "AG_DataSource *ds" "const char *magic" "const AG_Version *verRequired" "AG_Version *verRead"
.Pp
.Ft "void"
.Fn AG_WriteVersion "AG_DataSource *ds" "const char *magic" "const AG_Version *ver"
.Pp
.Ft "int"
.Fn AG_ReadObjectVersion "AG_DataSource *ds" "AG_Object *obj"
.Pp
.Ft "void"
.Fn AG_WriteObjectVersion "AG_DataSource *ds" "const AG_Object *obj"
.Pp
.nr nS 0
The
.Fn AG_ReadVersion
function reads version information from
.Fa ds
and returns 0 if the following data is binary compatible against the version
represented by
.Fa verRequired ,
or -1 if the data is not compatible.
If
.Fa verRead
is not NULL, it is set to the version information read from
.Fa ds .
.Pp
.Fn AG_WriteVersion
writes version information from
.Fa ver
to
.Fa ds .
.Pp
The
.Fn AG_ReadObjectVersion
and
.Fn AG_WriteObjectVersion
variants use the version number from the class description structure
and sets the signature to the name of the class (see
.Xr AG_ObjectClass 3 ) .
.Sh EXAMPLES
The following code writes version information to a data stream:
.Bd -literal -offset indent
.\" SYNTAX(c)
AG_DataSource *ds;
AG_Version ver;

ver.major = 1;
ver.minor = 1;
AG_WriteVersion(ds, "My-Magic", &ver);
.Ed
.Pp
The following code reads version information from a data stream:
.Bd -literal -offset indent
.\" SYNTAX(c)
AG_DataSource *ds;
AG_Version verRequired, ver;

verRequired.major = 1;
verRequired.minor = 0;
if (AG_ReadVersion(ds, "My-Magic", &verRequired,
    &ver) == 0) {
	AG_Verbose("Version OK! (%u.%u)\\n",
	    ver.major, ver.minor);
} else {
	AG_Verbose("Version not OK!\\n");
}
.Ed
.Pp
.Sh SEE ALSO
.Xr AG_DataSource 3 ,
.Xr AG_Intro 3
.Sh HISTORY
The
.Nm
interface first appeared in Agar 1.0