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! 3: <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>6. Validating callback functions</title><link rel="stylesheet" href="tutorial.css" type="text/css" /><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="libConfuse tutorial" /><link rel="up" href="index.html" title="libConfuse tutorial" /><link rel="prev" href="ar01s05.html" title="5. Parsing from internal buffers" /><link rel="next" href="ar01s07.html" title="7. Value parsing callback" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">6. Validating callback functions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ar01s05.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ar01s07.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="6. Validating callback functions"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id442168"></a>6. Validating callback functions</h2></div></div></div><p>
! 4: Remember the problem about a negative or too large "repeat" value
! 5: in <a class="xref" href="ar01s02.html#negative-repeat-problem">Section 2, “Other types of options”</a>? The code that prints
! 6: the greeting has those lines:
! 7: </p><pre class="programlisting">
! 8: ...
! 9: repeat = cfg_getint(cfg_greet, "repeat");
! 10: while(repeat--)
! 11: ...
! 12: </pre><p>
! 13: The repeat variable is defined as an int, a signed integer. If the user
! 14: specified a negative repeat value in the configuration file, this code
! 15: would continue to decrease the repeat variable until it eventually
! 16: underflowed.
! 17: </p><p>
! 18: We'll fix this by not allowing a negative value in the configuration
! 19: file. Of course we could first just check if the value is negative
! 20: and then abort, using <code class="function">cfg_getint()</code> and a test.
! 21: But we will use a validating callback function instead. This way
! 22: <code class="function">cfg_parse()</code> will return an error directly when
! 23: parsing the file, additionally indicating on which line the error
! 24: is.
! 25: </p><p>
! 26: A validating callback function is defined as:
! 27: </p><pre class="programlisting">
! 28: typedef int (*cfg_validate_callback_t)(cfg_t *cfg, cfg_opt_t *opt);
! 29: </pre><p>
! 30: This function takes two arguments: the section and the option. It
! 31: should return 0 on success (ie, the value validated ok). All other
! 32: values indicates an error, and the parsing is aborted. The callback
! 33: function should notify the error itself, for example by calling
! 34: <code class="function">cfg_error()</code>.
! 35: </p><p>
! 36: Here is the code for the callback function:
! 37: </p><a id="listing7"></a><pre class="programlisting">
! 38: 1 int validate_unsigned_int(cfg_t *cfg, cfg_opt_t *opt)
! 39: 2 {
! 40: 3 int value = cfg_opt_getnint(opt, cfg_opt_size(opt) - 1);
! 41: 4 if(value < 0)
! 42: 5 {
! 43: 6 cfg_error(cfg, "integer option '%s' must be positive in section '%s'",
! 44: 7 opt->name, cfg->name);
! 45: 8 return -1;
! 46: 9 }
! 47: 10 return 0;
! 48: 11 }
! 49: 12
! 50: </pre><p>
! 51: Only the last value is validated, because libConfuse will call this
! 52: function once for every value corresponding to the option. Since
! 53: the "repeat" option is not a list, we could instead have used
! 54: <code class="function">cfg_opt_getint(opt)</code> to retrieve the only
! 55: value. However, if we later want to use this callback to validate
! 56: an integer list, it is already lists-aware.
! 57: </p><div class="sect2" title="6.1. Installing the callback"><div class="titlepage"><div><div><h3 class="title"><a id="id442390"></a>6.1. Installing the callback</h3></div></div></div><p>
! 58: The validating callback is installed with
! 59: <code class="function">cfg_set_validate_func()</code>. It is called with
! 60: a string specifying which option is affected, and a pointer to
! 61: the callback function. To specify an option in a subsection,
! 62: the section and the option must be separated with a vertical
! 63: bar ("|").
! 64: </p><p>
! 65: We're now also looking at the return code from
! 66: <code class="function">cfg_parse()</code> to verify that the parsing was
! 67: successful. The complete program is now:
! 68: </p><a id="listing8"></a><pre class="programlisting">
! 69: 1 #include <stdio.h>
! 70: 2 #include <confuse.h>
! 71: 3
! 72: 4 int validate_unsigned_int(cfg_t *cfg, cfg_opt_t *opt)
! 73: 5 {
! 74: 6 int value = cfg_opt_getnint(opt, cfg_opt_size(opt) - 1);
! 75: 7 if(value < 0)
! 76: 8 {
! 77: 9 cfg_error(cfg, "integer option '%s' must be positive in section '%s'",
! 78: 10 opt->name, cfg->name);
! 79: 11 return -1;
! 80: 12 }
! 81: 13 return 0;
! 82: 14 }
! 83: 15
! 84: 16 int main(void)
! 85: 17 {
! 86: 18 cfg_opt_t greet_opts[] =
! 87: 19 {
! 88: 20 CFG_STR_LIST("targets", "{World}", CFGF_NONE),
! 89: 21 CFG_INT("repeat", 1, CFGF_NONE),
! 90: 22 CFG_END()
! 91: 23 };
! 92: 24 cfg_opt_t opts[] =
! 93: 25 {
! 94: 26 CFG_SEC("greeting", greet_opts, CFGF_TITLE | CFGF_MULTI),
! 95: 27 CFG_END()
! 96: 28 };
! 97: 29 cfg_t *cfg, *cfg_greet;
! 98: 30 int repeat;
! 99: 31 int i, j;
! 100: 32
! 101: 33 cfg = cfg_init(opts, CFGF_NONE);
! 102: 34 cfg_set_validate_func(cfg, "greeting|repeat", validate_unsigned_int);
! 103: 35 if(cfg_parse(cfg, "hello.conf") == CFG_PARSE_ERROR)
! 104: 36 return 1;
! 105: 37
! 106: 38 for(j = 0; j < cfg_size(cfg, "greeting"); j++)
! 107: 39 {
! 108: 40 cfg_greet = cfg_getnsec(cfg, "greeting", j);
! 109: 41
! 110: 42 repeat = cfg_getint(cfg_greet, "repeat");
! 111: 43 while(repeat--)
! 112: 44 {
! 113: 45 printf("%s", cfg_title(cfg_greet));
! 114: 46 for(i = 0; i < cfg_size(cfg_greet, "targets"); i++)
! 115: 47 printf(", %s", cfg_getnstr(cfg_greet, "targets", i));
! 116: 48 printf("!\n");
! 117: 49 }
! 118: 50 }
! 119: 51
! 120: 52 cfg_free(cfg);
! 121: 53 return 0;
! 122: 54 }
! 123: 55
! 124: </pre></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ar01s05.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ar01s07.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">5. Parsing from internal buffers </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 7. Value parsing callback</td></tr></table></div></body></html>
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