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<h2>
<a name="1205177"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">extern</font>
</h2><hr>
<p>
<a name="1242556"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">Define symbol as external</font>
</p>
<h3>
<a name="1205178"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">Syntax</font>
</h3>
<a name="1205179"> </a><font size=2 face=Courier><strong>extern symbol [weak] [realname <font size=2 face=Courier><strong><em>string</em></strong></font>] [origin <font size=2 face=Courier><strong><em>string</em></strong></font>] [datausage]<br>牋牋牋牋牋牋牋燵routineusage] [notypeusage]<br></strong></font>
<h3>
<a name="1205180"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">Description</font>
</h3>
<p>
<a name="1205181"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The <font size=2 face=Courier><strong>extern</strong></font> directive is used to declare the <font size=2 face=Courier><strong><em>symbol</em></strong></font> as external to the current module. An example of its use is to call an external routine.</font>
</p>
<p>
<a name="1205182"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The optional <font size=2 face=Courier><strong>weak</strong></font> argument indicates that a weak reference is to be made to the symbol. <font size=2 face=Courier><strong>weak</strong></font> references do not force the linker to resolve the reference. They are used for example, to resolve debug information, but do not cause the linker to pull in extra library modules simply to resolve debug information.</font>
</p>
<p>
<a name="1205183"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The name used for the symbol in the object file is the same as the name of the symbol in the assembly source file, unless <font size=2 face=Courier><strong>realname</strong></font> is specified. In this case the name used for the symbol in the object file is the name specified by the string argument to <font size=2 face=Courier><strong>realname</strong></font>.</font>
</p>
<p>
<a name="1205184"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif"><font size=2 face=Courier><strong>origin</strong></font> enables an origin to be specified for the symbol in the object file. This allows the linker to ensure that only a definition of a symbol with the same name and the same origin matches this external reference. If <font size=2 face=Courier><strong>origin</strong></font> is not specified, then the symbol in the object file is not given a specific origin. The linker can match this external reference with a definition of a symbol with the same name and any origin.</font>
</p>
<p>
<a name="1205185"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The three optional arguments <font size=2 face=Courier><strong>datausage</strong></font>, <font size=2 face=Courier><strong>routineusage</strong></font> and <font size=2 face=Courier><strong>notypeusage</strong></font> generate extra symbol information in the object file, which can be incorporated by the linker into a symbol table. This may be used by tools such as a debugger or profiler, when reading symbol information.</font>
</p>
<p>
<a name="1205186"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif"><b><font size=2 face=Courier><strong>datausage</strong></font></b></font>
<br>
<dl><dl> <dl>
<dt> <a name="1229742"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">Indicates that the symbol is associated with a data object.</font>
</dl>
</dl></dl>
<p>
<a name="1229434"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif"><b><font size=2 face=Courier><strong>routineusage</strong></font></b></font>
<br>
<dl><dl> <dl>
<dt> <a name="1229743"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">Indicates that the symbol is associated with a routine.</font>
</dl>
</dl></dl>
<p>
<a name="1229436"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif"><b><font size=2 face=Courier><strong>notypeusage</strong></font></b></font>
<br>
<dl><dl> <dl>
<dt> <a name="1229744"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">Indicates that the symbol type (data or routine) is not specified.</font>
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