put.so

berkeley db 4.6.21的源码。berkeley db是一个简单的数据库管理系统

m4_comment([$Id: put.so,v 1.11 2003/10/18 19:16:15 bostic Exp $])

m4_ref_title(Upgrading m4_db Applications,
    Release 3.1: DB-__GT__put,,
    upgrade.3.1/set_paniccall, upgrade.3.1/dup)

m4_p([dnl
For the Queue and Recno access methods, when the m4_ref(DB_APPEND) flag
is specified to the m4_refT(dbh_put), the allocated record number is
returned to the application in the m4_arg(key) m4_ref(Dbt) argument.  In
previous releases of m4_db, this m4_ref(Dbt) structure did not follow
the usual m4_ref(Dbt) conventions.  For example, it was not possible to
cause m4_db to allocate space for the returned record number.  Rather,
it was always assumed that the m4_arg(data) field of the m4_arg(key)
structure referred to memory that could be used as storage for a
db_recno_t type.])

m4_p([dnl
As of the m4_db 3.1.0 release, the m4_arg(key) structure behaves as
described in the m4_ref(Dbt) C++/Java class or C structure documentation.])

m4_p([dnl
Applications which are using the m4_ref(DB_APPEND) flag for Queue and
Recno access method databases will require a change to upgrade to the
m4_db 3.1 releases.  The simplest change is likely to be to add the
m4_ref(DB_DBT_USERMEM) flag to the m4_arg(key) structure.  For example,
code that appears as follows:])

m4_indent([dnl
DBT key;
db_recno_t recno;
m4_blank
memset(&key, 0, sizeof(DBT));
key.data = &recno;
key.size = sizeof(recno);
DB-__GT__put(DB, NULL, &key, &data, DB_APPEND);
printf("new record number is %lu\n", (u_long)recno);])

m4_p([would be changed to:])

m4_indent([dnl
DBT key;
db_recno_t recno;
m4_blank
memset(&key, 0, sizeof(DBT));
key.data = &recno;
key.ulen = sizeof(recno);
key.flags = DB_DBT_USERMEM;
DB-__GT__put(DB, NULL, &key, &data, DB_APPEND);
printf("new record number is %lu\n", (u_long)recno);])

m4_p([dnl
Note that the m4_arg(ulen) field is now set as well as the flag value.
An alternative change would be:])

m4_indent([dnl
DBT key;
db_recno_t recno;
m4_blank
memset(&key, 0, sizeof(DBT));
DB-__GT__put(DB, NULL, &key, &data, DB_APPEND);
recno = *(db_recno_t *)key-__GT__data;
printf("new record number is %lu\n", (u_long)recno);])

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