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<h1 class="topictitle1">Apply overrides when compiling a program</h1>
<div><p>Overrides can be applied at the time a program is being compiled
for either of two purposes: to select the source file, or to provide external
data definitions for the compiler to use in defining the record formats to
be used on I/O operations.</p>
<p>Overrides to the source file are handled just like any other
override. They can select another file, another member of a database file,
another label for diskette or tape, or change other file attributes.</p>
<p>You can also apply overrides to files that are used within the program
being compiled, if they are being used as externally described files in the
program. These files are not opened at compile time, and thus the overrides
are not applied in the normal manner. These overrides are used at compile
time only to determine the file name and library that will be used to define
the record formats and fields for the program to use I/O operations. Any
other file attributes specified on the override are ignored at compile time. It is necessary that these file overrides be active at compile time only
if the file name specified in the source for the program is not the file name
that contains the record formats that the application needs.</p>
<p>The file name that is opened when the compiled program is run is determined
by the file name that the program source refers to, changed by whatever overrides
are in effect at the time the program runs. The file name used at compile
time is not kept. The record formats in the file that is actually opened
must be compatible with those that were used when the program was compiled. Obviously, the easiest way to assure that records are compatible is to have
the same overrides active at run time that were active at compile time. If
your program uses externally described data and a different field level file
is used at run time, it is typically necessary to specify LVLCHK(*NO) on the
override. See <a href="rbal3redirect.htm#rbal3redirect">Redirect files</a> for details.</p>
<p>The following example shows how overrides work when compiling a program:</p>
<div class="fignone"><span class="figcap">Figure 1. An example over overrides when compiling a program</span>. <span class="figdesc">The
following example shows how overrides work when compiling a program.</span><p>Override 1    <span><samp class="codeph">OVRDBF FILE(RPGSRC) +</samp></span><br />
                      <span><samp class="codeph">TOFILE(SRCPGMS) MBR(INVN42)</samp></span><br />
Override 2    <span><samp class="codeph">OVRPRTF FILE(OUTPUT) TOFILE(REPORTS)</samp></span><br />
                  <span><samp class="codeph">CALL PGM(A)</samp></span><br />
<br />
                         Program A<br />
Override 3           <span><samp class="codeph">OVRPRTF FILE(LISTOUT) +</samp></span><br />
                              <span><samp class="codeph">TOFILE(OUTPUT)</samp></span><br />
Override 4           <span><samp class="codeph">OVRDBF FILE(RPGSRC) WAITFILE(30)</samp></span><br />
                         <span><samp class="codeph">CRTRPGPGM PGM(INVENTORY) +</samp></span><br />
                              <span><samp class="codeph">SRCFILE(RPGSRC)</samp></span><br />
                          <span><samp class="codeph">RETURN</samp></span><br />
<br />
Override 5    <span><samp class="codeph">OVRPRTF FILE(LISTOUT) +</samp></span><br />
                       <span><samp class="codeph">TOFILE(REPORTS) LPI(8)</samp></span><br />
                  <span><samp class="codeph">CALL PGM(INVENTORY)</samp></span></p>
</div>
<p>The program INVENTORY opens the printer file REPORTS in place of printer
file LISTOUT and creates output at 8 lines per inch.</p>
<p>The program INVENTORY is created (compiled) from the member INVN42 in the
database file SRCPGMS. Override 4, which is applied first, overrides an optional
file attribute. Override 1, which is applied last, causes the file RPGSRC
to be overridden with the database file SRCPGMS, member INVN42.</p>
<p>The program INVENTORY is created with the printer formats from the file
REPORTS. Assume that the source for the program INVENTORY, which is taken
from file SRCPGMS and member INVN42, contains an open to the printer file
LISTOUT. Override 3, which is applied first, causes the file LISTOUT to be
overridden with OUTPUT. Override 2, which is applied last, overrides OUTPUT
with REPORTS. Other attributes can be specified here, but it is not necessary
because only the record formats are used at compile time.</p>
<p>At run time, override 3 is no longer active, because program A has ended. Therefore override 2 has no effect on LISTOUT. However, override 5, which
is active at run time, replaces LISTOUT with REPORTS and specifies 8 lines
per inch. Because the same file is used for compilation and run-time, you
can leave level checking on.</p>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbal3applyovr.htm" title="You can perform two general types of overrides, which are file overrides and overrides for program device entries.">Apply overrides</a></div>
</div>
<div class="relref"><strong>Related reference</strong><br />
<div><a href="rbal3eoscd.htm" title="Some commands ignore overrides entirely, while others allow overrides only for certain parameters.">Effect of overrides on some commands</a></div>
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