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<h1>FtpSetCallback</h1>
<p>Establishes a callback function.</p>
<h2>SYNOPSIS</h2>
<pre>
#include &lt;ftplib.h&gt;
int FtpCallback(FtpCallbackOptions *opt, netbuf *nControl);
</pre>
<p>FtpCallbackOptions is declared as follows.</p>
<pre>
typedef struct FtpCallbackOptions {
    FtpCallback cbFunc;		/* function to call */
    void *cbArg;		/* argument to pass to function */
    unsigned int bytesXferred;	/* callback if this number of bytes transferred */
    unsigned int idleTime;	/* callback if this many milliseconds have elapsed */
} FtpCallbackOptions;
</pre>
<h2>PARAMETERS</h2>
<dl>
<dt><b>opt</b></dt>
<dd>The address of a structure that contains a pointer to the callback
  function and the criteria for calling it.</dd>
<dt><b>nControl</b></dt>
<dd>A handle returned by <a href="FtpConnect.html">FtpConnect()</a>
or <a href="FtpAccess.html">FtpAccess()</a>.</dd>
</dl>
<h2>DESCRIPTION</h2>
<p>FtpSetCallback() establishes a callback functions and tells FTPlib
  when to call it. A data connection inherits the options assigned to
  the control connection it is created from. Callbacks are only called
  on file data connections.</p>
<p>The fields in FtpCallbackStruct are described below.</p>
<dl>
<dt>cbFunc</dt>
<dd>Specifies the address of a user callback routine.</dd>
<dt>cbArg</dt>
<dd>Specifies an argument to pass to the user's callback
routine.</dd>
<dt>idleTime</dt>
<dd>Specifies the socket idle time in milliseconds that triggers
calling the user's callback routine.</dd>
<dt>bytesXferred</dt>
<dd>Specifies the number of bytes to transfer between calls to the
user's callback routine.</dd>
</dl>
<p>The user's callback routine is specified as:</p>
<pre>
typedef int (*FtpCallback)(netbuf *nControl, int xfered, void *arg);
</pre>
<b>nControl</b> is the data connection in use. <b>xfered</b> specifies
how many bytes of data have been transferred on the
connection. <b>arg</b> is the value passed in the FtpCallbackOptions
field cbArg.
<p>The user can request to be called back on either of two
events.</p>
<p>If the routine should be called when the data socket is idle for
some period of time, pass the number of milliseconds of inactivity
that should trigger a callback in the idleTime field.</p>
<p>If the routine should be called when a certain amount of data has
been transferred, specify a non-zero value in bytesXferred.  This
value represents the minimum number of bytes to transfer between
callbacks. When using this option, ftplib keeps track of the number of
bytes transferred and calls the user once the specified number of
bytes or more has been transferred. It then resets the count to 0 and
starts again.</p>
<p>If the user wishes to continue the transfer, the callback
routine should return true (non-zero). It can abort the transfer by
return zero.</p>
<h2>RETURN VALUE</h2>
<p>Returns 1 for success or 0 for failure.</p>
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