tdb_firstkey.3

Linux下的一个关系数据库源代码

.TH tdb_firskey "Aug 16, 2000" "Samba" "Linux Programmer's Manual"
.SH NAME
tdb_firstkey - return the key of the first record in a tdb database
tdb_nextkey - return the key of next record in the tdb database
.SH SYNOPSIS
.nf
.B #include <tdb.h>
.sp
.BI "TDB_DATA tdb_firstkey(TDB_CONTEXT *" tdb ");"
.BI "TDB_DATA tdb_nextkey(TDB_CONTEXT *" tdb ", TDB_DATA " prev_key ");"
.sp
.SH DESCRIPTION
.I tdb_firstkey 
fetches the key of the first entry in the 
.I tdb 
database.
.I tdb_nextkey
fetches the key of the entry immediately after 
.I prev_key
in the database.
.sp 
The TDB_DATA structure returned by both these functions is defined as:
.PP
.RS
.nf
typedef struct {
	char *dptr;
	size_t dsize;
} TDB_DATA;
.fi
.RE
.PP
.sp
The order in which this traverses the database is its own internal
hash order. Do not expect the keys to be in any recognizably sorted
order.
.sp
These functions are reliable even if other writers are accessing the
database (or you are replacing or deleting elements as you traverse),
except in the case of nested
.I tdb_firstkey
or
.I tdb_nextkey
calls.  For example, the following outer traversal may fail to
traverse all the elements, or may even traverse elements twice if
other processes are manipulating the database:
.PP
.RS
.nf
	TDB_DATA i, j;

	for (i = tdb_firstkey(tdb); i.dptr; i = tdb_nextkey(tdb, i)) {
		for (j = tdb_firstkey(tdb); j.dptr; j = tdb_nextkey(tdb, j)) {
		...
		}
	}
.fi
.RE
.PP
If such behaviour is desired, use
.I tdb_traverse
instead.
.sp
.SH "RETURN VALUE"
If the call succeeds, then a TDB_DATA structure is returned with the
.I dptr 
structure filled in. If the call fails or you have reached the end of
the database then
.I dptr 
will be set to NULL.
.sp
.B NOTE:
The caller is responsible for freeing the data pointed to by
.I dptr
.
.SH AUTHORS
Software: Andrew Tridgell <[e-mail]> and 
Luke Kenneth Casson Leighton
Man page: Ben Woodard <[e-mail]>
.SH "SEE ALSO"
.BR gdbm (3),
.BR tdb(3)