ug_ch11.htm

来自「db.* (pronounced dee-be star) is an adva」· HTM 代码 · 共 693 行 · 第 1/2 页

<p><b><font size="2">d_recread</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_trbegin</font></b></p>
</td>
</tr>
<tr>
<td width="28%" valign="top">
<p><b><font size="2">d_dbdpath</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_keyfind</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_recset</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_trend</font></b></p>
</td>
</tr>
<tr>
<td width="28%" valign="top">
<p><b><font size="2">d_dbfpath</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_keyfree</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_recwrite</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_wrcurr</font></b></p>
</td>
</tr>
<tr>
<td width="28%" valign="top">
<p><b><font size="2">d_dblog</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_keyfrst</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_renfile</font></b></p>
</td>
<td width="24%" valign="top">&nbsp;</td>
</tr>
<tr>
<td width="28%" valign="top">
<p><b><font size="2">d_dbtaf</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_keylast</font></b></p>
</td>
<td width="24%" valign="top">
<p><b><font size="2">d_rlbclr</font></b></p>
</td>
<td width="24%" valign="top">&nbsp;</td>
</tr>
</table>
<h2><a name="Commands" id="Commands"></a>11.6 dal-Specific
Commands</h2>
<p><font size="2">This section describes how variables are defined
for <b>dal</b> and explains the <b>dal</b>-specific commands that
help make the utility more useful as a learning and prototyping
tool.</font></p>
<hr>
<h3><a name="def_rec" id="def_rec"></a>def_rec, def_fld</h3>
<p><font size="2">Variables are defined in one of two
ways:</font></p>
<p>1. <i>Implicitly</i> : A variable can be created from the
context of a statement. The statement below causes a variable named
"<b>per</b>" to be defined as the same type as the current
record.</p>
<pre>
<font color="#0000FF">keyfind(pers_name,"Norm");
recread(per);</font>
</pre>
<p><font size="2">The next statement causes a variable named
"<b>addr</b>" to be defined as a field with the same type as the
"<b>pers_addr</b>" field in the schema.</font></p>
<pre>
<font color="#0000FF">crread(pers_addr,addr);</font>
</pre>
<p><font size="2">The following statement causes a variable named
"<b>dba</b>" to be defined as type <b>DB_ADDR.</b></font></p>
<pre>
<font color="#0000FF">crget(dba);</font>
</pre>
<p><font size="2">2. <i>Explicitly</i> : Two functions are provided
to explicitly create and type record or field variables:</font></p>
<pre>
<font color="#0000FF">def_rec(rec_type,var_name);</font>
</pre>
<p><font size="2">or</font></p>
<pre>
<font color="#0000FF">def_fld(fld_type,var_name);</font>
</pre>
<p><font size="2">The <b>def_rec</b> function creates a variable
(named <b>var_name</b>) that is defined with the same type as the
record specified by <b>rec_type</b>. <b>def_fld</b> creates a
variable (named <b>var_name</b>) that is defined with the same type
as the field specified by <b>fld_type</b>.</font></p>
<hr>
<h3><a name="abort" id="abort"></a>abort</h3>
<p><font size="2">Exit <b>dal</b> immediately without closing
database</font></p>
<h5>Summary</h5>
<pre>
<font color="#0000FF">abort;</font>
</pre>
<h5>Description</h5>
<p><font size="2">This command causes <b>dal</b> to stop
immediately without closing the database. Any data remaining in the
<b><i>db.*</i></b> cache will not be written to the database. If
you have created only a few changes or additions (such that all the
data fits into the cache), then none of your work will be saved.
However, be aware that indiscriminate use of the <b>abort</b>
command can lead to database corruption in the event that some
changes get written to disk while the remaining are lost when you
abort. You must be concerned about this only if you are not using
transactions.</font></p>
<hr>
<h3><a name="curr" id="curr"></a>curr</h3>
<p><font size="2">Print the currency tables.</font></p>
<h5>Summary</h5>
<pre>
<font color="#0000FF">curr;</font>
</pre>
<h5>Description</h5>
<p><font size="2">This command causes <b>dal</b> to print out the
currency tables, showing current database, current record, and
current owners and members for each set.</font></p>
<hr>
<h3><a name="exit" id="exit"></a>exit</h3>
<p><font size="2">Exit <b>dal</b>.</font></p>
<h5>Summary</h5>
<pre>
<font color="#0000FF">exit;</font>
</pre>
<h5>Description</h5>
<p><font size="2">This command calls <b>d_close</b> to close the
database, and exit with a code of zero (that is, call
exit).</font></p>
<hr>
<h3><a name="input" id="input"></a>input</h3>
<p><font size="2">Read values into a variable.</font></p>
<h5>Summary</h5>
<pre>
<font color=
"#0000FF">input [(filename)] var_name [,var_name ]...;</font>
</pre>
<h5>Description</h5>
<p><font size="2">This command reads variable values from the
keyboard or a file. If a variable is a record, then the individual
field values will be requested with separate prompts. If a file
name is specified for input, one line from the file will be read
for each variable listed. File names must be enclosed in quotes.
Fields within a line are in fixed format with the following lengths
for different field types:</font></p>
<table border="1" cellspacing="1" cellpadding="7" width="295">
<tr>
<td width="35%" valign="top">
<p><b><font face="Palatino" size="2">Char</font></b></p>
</td>
<td width="65%" valign="top">
<p><b><font face="Palatino" size="2">Length specified in
schema</font></b></p>
</td>
</tr>
<tr>
<td width="35%" valign="top">
<p><b><font face="Palatino" size="2">int</font></b></p>
</td>
<td width="65%" valign="top">
<p><font face="Palatino" size="2">6</font></p>
</td>
</tr>
<tr>
<td width="35%" valign="top">
<p><b><font face="Palatino" size="2">short</font></b></p>
</td>
<td width="65%" valign="top">
<p><font face="Palatino" size="2">6</font></p>
</td>
</tr>
<tr>
<td width="35%" valign="top">
<p><b><font face="Palatino" size="2">long</font></b></p>
</td>
<td width="65%" valign="top">
<p><font face="Palatino" size="2">10</font></p>
</td>
</tr>
<tr>
<td width="35%" valign="top">
<p><b><font face="Palatino" size="2">float</font></b></p>
</td>
<td width="65%" valign="top">
<p><font face="Palatino" size="2">10</font></p>
</td>
</tr>
<tr>
<td width="35%" valign="top">
<p><b><font face="Palatino" size="2">double</font></b></p>
</td>
<td width="65%" valign="top">
<p><font face="Palatino" size="2">10</font></p>
</td>
</tr>
</table>
<p><font size="2">Note that these widths are the same as those
created by the <b>print</b> command.</font></p>
<h5>Examples</h5>
<pre>
<font color="#0000FF">open("tims","o");
def_rec(author,a);
input a;            /* Get data from terminal */;
fillnew(author,a);
input ("auth.imp");      /* Get data from file */;
fillnew(author,a);</font>
</pre>
<h5>Diagnostics</h5>
<p><font size="2">Errors can occur when input reads from a file and
the line lengths in the file are inconsistent.</font></p>
<hr>
<h3><a name="print" id="print"></a>print</h3>
<p><font size="2">Print values from a variable list.</font></p>
<h5>Summary</h5>
<pre>
<font color=
"#0000FF">print [(filename)] var_name [,var_name ...];</font>
</pre>
<h5>Description</h5>
<p><font size="2">This command prints one line of data to the
terminal or to a file. If a variable is a record, then the
individual field values will be printed, with no spaces between the
values, each field width being determined by the field type (see
table under input). Literal strings may be included in the
<i>var_name</i> list. If a file name is specified for output, one
line will be written to the file for each print command. File names
must be enclosed in quotes. If an output file is used within an
input command, the file is re-opened for input.</font></p>
<h5>Examples</h5>
<pre>
<font color="#0000FF">open("tims","o");
findfm(author_list);
recread(a);
print "author:",a;
crget(dba);
print("author.lst") "dba:",dba,"author:",author;</font>
</pre>
<hr>
<h3><a name="rewind" id="rewind"></a>rewind</h3>
<p><font size="2">Rewind (or reset back to the beginning of) a
file.</font></p>
<h5>Summary</h5>
<pre>
<font color="#0000FF">rewind "<i>filename</i>";</font>
</pre>
<h5>Description</h5>
<p><font size="2">This command rewinds a file. If the file was
opened for reading, then subsequent reads will start from the
beginning (that is, the first line will be reread). If the file was
opened for writing, it will be truncated and all previous data will
be lost.</font></p>
<hr>
<h3><a name="schema" id="schema"></a>schema</h3>
<p><font size="2">Print schema information.</font></p>
<h5>Summary</h5>
<pre>
<font color="#0000FF">schema <i>[spec]</i>;</font>
</pre>
<h5>Description</h5>
<p><font size="2">This command prints information about a database
schema, including the record types, field types, and set
information. The <b>schema</b> command with no arguments produces a
list of the record names and set names. If <i>spec</i> is a record,
then detailed information about the record is printed, including a
list of the fields, and the field information for each field. If
<i>spec</i> is a field name, then the type and length is printed.
Additionally, if the field is a key, then the kind of key, and the
key file containing the key is printed. If <i>spec</i> is a set
name, then order, owner type, member type(s), and sorting
information is printed.</font></p>
<hr>
<h3><a name="whileok" id="whileok"></a>whileok</h3>
<p><font size="2">Repeat statements while (<b>db_status</b> ==
S_OKAY).</font></p>
<h5>Summary</h5>
<pre>
<font color="#0000FF">whileok {
   statements;
      ...
}</font>
</pre>
<h5>Description</h5>
<p><font size="2">This command functions in the same manner as the
following C code:</font></p>
<pre>
<font color="#0000FF">while (db_status == S_OKAY) {
   statements;
   ...
}</font>
</pre>
<p><font size="2">Note that <b>whileok</b> statements can be
nested.</font></p>
<h5>Examples</h5>
<pre>
<font color="#0000FF">/* List all authors and their publications */
open("tims","o");
findfm(author_list);
whileok {
   recread(a);
   print "Author:",a;
   setor(has_published);
   findfm(has_published);
   whileok {
      recread(b);
      print "Published:",b;
      findnm(has_published);
   }
   findnm(author_list);
}</font>
</pre>
<h2><a name="Limitations" id="Limitations"></a>11.7 dal
Limitations</h2>
<p><font size="2">The following is a list of <b><i>db.*</i></b>
functions and functionalities <i>not</i> supported by
<b>dal</b>:</font></p>
<p><font size="2">1. Group locking function (that is,
<b>d_lock()</b>)<br>
2. Timestamping functions<br>
3. Currency functions (<b>d_rdcurr()</b>, <b>d_rerdcurr()</b>, and
<b>d_wrcurr()</b>)<br>
4. File rename functions (<b>d_renfile()</b> and
<b>d_renclean()</b>)<br>
5. Alternate initialization file location
(<b>d_dbini()</b>)</font></p>
<p><font size="2">In addition,</font></p>
<p><font size="2">1. <b>dal</b> does not support multiple
databases.<br>
2. <b>dal</b> does not support arrays.</font></p>
<p><a href="UG_Ch12.htm">Next Page</a></p>
</body>
</html>