reeves.htm

高效c++编程

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const long null = 0L;          // see <SCRIPT>sendmetoo(25,6292,'E');</SCRIPT> ONMOUSEOVER = "self.status = 'Item E25'; return true" ONMOUSEOUT = "self.status = self.defaultStatus">Item E25</A> for a discussion
                               // of this approach
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<A NAME="dingp27"></A><LI>I have adopted a commenting convention of <CODE>//&gt;x</CODE> to indicate places in a function where exceptions are possible.  Like any manual approach, this technique is error prone and very likely to miss something.  It is better than nothing, however, and I have found it useful.<SCRIPT>create_link(27);</SCRIPT>


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<P><A NAME="dingp28"></A><A NAME="AUTO00018"></A>The following table summarizes the goals and guidelines that are presented in the next <NOBR>section.<SCRIPT>create_link(28);</SCRIPT>
</NOBR></P>
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<TABLE ALIGN="center" WIDTH="95%" CELLSPACING="2" CELLPADDING="2" BGCOLOR="#FFFFCC" BORDER="0">
<TR><TH COLSPAN="2" BGCOLOR="#000000"><FONT COLOR="#FFFFFF" FACE="Arial">Table: Goals and Guidelines</FONT></TH></TR>
<TR>
    <TD VALIGN="top"><B><a name="dingp29"></a><a href="./REEVES.HTM#goal1">I.</a></B></TD>
    <TD><B>When you propagate an exception, try to leave the object in the state it had when the function was entered.</B><SCRIPT>create_link(29,'#FFFFCC');</SCRIPT>

<OL VALUE="1">
<A NAME="dingp30"></A>
        <LI> <a href="./REEVES.HTM#guide1">Make sure your <CODE>const</CODE> functions really 
          are <CODE>const</CODE>.</a><SCRIPT>create_link(30,'#FFFFCC');</SCRIPT></nobr>

<A NAME="AUTO00020"></A>
<A NAME="dingp31"></A>
        <LI> <a href="./REEVES.HTM#guide2">Perform exception prone operations early, and/or 
          through temporaries.</a><SCRIPT>create_link(31,'#FFFFCC');</SCRIPT>

<A NAME="AUTO00021"></A>
<A NAME="dingp32"></A>
        <LI> <a href="./REEVES.HTM#guide3">Watch out for side effects in expressions that 
          might propagate exceptions.</a><SCRIPT>create_link(32,'#FFFFCC');</SCRIPT>

<BR>

</OL></TD></TR>
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    <TD VALIGN="top"><A NAME="dingp33"></A><B><a href="./REEVES.HTM#goal2">II.</a></B></TD>
    <TD><B>If you can not leave the object in the same state it was in when the function was entered, try to leave it in a good state.</B><SCRIPT>create_link(33,'#FFFFCC');</SCRIPT>


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	<OL TYPE="1">
      <A NAME="dingp34"></A>
        <LI VALUE="4"> <a href="./REEVES.HTM#guide4">Either reinitialize the object, or mark 
          it internally to indicate that it is no longer usable but might be recovered.</a><SCRIPT>create_link(34,'#FFFFCC');</SCRIPT>


</OL>

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</TD></TR>
<TR>
    <TD VALIGN="top"><A NAME="dingp35"></A><B><a href="./REEVES.HTM#goal3">III.</a></B></TD>
    <TD><B>If you can not leave the object in a &quot;good&quot; state, make sure the destructor will still work.</B><SCRIPT>create_link(35,'#FFFFCC');</SCRIPT>


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   <OL TYPE="1">
      <A NAME="dingp36"></A>
        <LI VALUE="5"><a href="./REEVES.HTM#guide5">Do not leave dangling pointers in your 
          objects. Delete pointers through temporaries.</a><SCRIPT>create_link(36,'#FFFFCC');</SCRIPT>


</OL>
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 </TD></TR>
<TR>
    <TD VALIGN="top"><A NAME="dingp37"></A><B><a href="./REEVES.HTM#goal4">IV.</a></B></TD>
    <TD><B>Avoid resource leaks.</B><SCRIPT>create_link(37,'#FFFFCC');</SCRIPT>

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    <OL TYPE="1">
<A NAME="AUTO00027"></A>
      <A NAME="dingp38"></A>
        <LI VALUE="6"><a href="./REEVES.HTM#guide6">If you have raw data pointers as members, 
          initialize them to null in the initializer list of your constructor(s), 
          then do necessary allocations in the constructor body where a catch 
          block can deal with potential resource leaks.</a><SCRIPT>create_link(38,'#FFFFCC');</SCRIPT>


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<A NAME="AUTO00028"></A>
</TD></TR>
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    <TD VALIGN="top"><A NAME="dingp39"></A><B><a href="./REEVES.HTM#goal5">V.</a></B></TD>
    <TD> <B>Do not catch any exception you do not have to.</B><SCRIPT>create_link(39,'#FFFFCC');</SCRIPT>


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    <OL TYPE="1">
<A NAME="AUTO00030"></A>
      <A NAME="dingp40"></A>
        <LI VALUE="7"><a href="./REEVES.HTM#guide7">Rewrite functions to preserve state, if 
          possible.</a><SCRIPT>create_link(40,'#FFFFCC');</SCRIPT>

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      <A NAME="dingp41"></A>
        <LI VALUE="8"><a href="./REEVES.HTM#guide8">Always use a catch <CODE>(...)</CODE> 
          <CODE>block</CODE> to cope with propagating exceptions.</a><SCRIPT>create_link(41,'#FFFFCC');</SCRIPT>

<A NAME="AUTO00032"></A>
      <A NAME="dingp42"></A>
        <LI VALUE="9"><a href="./REEVES.HTM#guide9">If you get stuck, call <CODE>terminate()</CODE>.</a><SCRIPT>create_link(42,'#FFFFCC');</SCRIPT>


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</TD></TR>
<TR>
    <TD VALIGN="top"><A NAME="dingp43"></A><B><a href="./REEVES.HTM#goal6">VI.</a></B></TD>
    <TD><B> Do not hide exception information from other parts of the program that
  might need it.</B><SCRIPT>create_link(43,'#FFFFCC');</SCRIPT>

<A NAME="AUTO00034"></A>
    <OL TYPE="1">
      <A NAME="dingp44"></A>
        <LI VALUE="10"> <a href="./REEVES.HTM#guide10">Always rethrow the exception caught 
          in a catch (<CODE>(...)</CODE> <CODE>block</CODE>).</a><SCRIPT>create_link(44,'#FFFFCC');</SCRIPT>

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      <A NAME="dingp45"></A>
        <LI VALUE="11"> <a href="./REEVES.HTM#guide11">Rethrow a different exception only 
          to provide additional information or capability.</a><SCRIPT>create_link(45,'#FFFFCC');</SCRIPT>

<A NAME="AUTO00036"></A>
      <A NAME="dingp46"></A>
        <LI VALUE="12"> <a href="./REEVES.HTM#guide12">Make sure one catch <CODE>block</CODE>