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<h3><a href="http://caterpillar.onlyfun.net/GossipCN/index.html">From
Gossip@caterpillar</a></h3>
<h1><a href="CppGossip.html">C++
Gossip: 标准例外类别</a></h1>
C++提供了标准的例外处理类别，所有的标准例外处理类别都衍生自exception类别，使用它必须包括exception标头档，而
exception类别衍生出来的logic_error类别与runtime_error类别在使用时，则必须包括stdexcept标头档，以下列出
exception与其衍生类别的继承架构： <br>
<div style="margin-left: 40px; font-family: Courier New,Courier,monospace;"><span style="font-weight: bold;">exception </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> bad_alloc </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> bad_exception </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> ios:base:failure </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> bad_cast </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> bad_typedid </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> logic_error </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> lehgth_error </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> domain_error </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> invalid_argument </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> out_of_range </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> runtime_error </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> overflow_error </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> range_error </span><br style="font-weight: bold;">
<span style="font-weight: bold;"> underflow_error</span><br>
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当错误发生而丢出例外物件时，您可以使用what()方法来取得错误讯息，这个错误讯息视您所采用的编译器而有所不同，下面这个程式故意存取超出字串范围的资料，以引发out_of_range例外并显示讯息： <br>
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<pre>#include <iostream> <br>#include <string> <br>#include <stdexcept> <br>using namespace std; <br><br>int main() { <br> try { <br> string str("caterpillar"); <br> cout << "str.substr(20, 2) = " <br> << str.substr(20, 2) <br> << endl; <br> } <br> catch(out_of_range e) { <br> cout << "错误: " <br> << e.what() <br> << endl; <br> } <br> <br> return 0;<br>}</pre>
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执行结果：</span><br>
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<td style="background-color: rgb(0, 0, 0);"><small><span style="color: rgb(255, 255, 255);">错误: basic_string::substr</span></small><span style="color: rgb(255, 255, 255);"><br>
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下面这个程式则是利用回圈不断配置记忆体，直到记忆体不足而发生bad_alloc例外为止，您可以观察到例外的捕捉与讯息：<br>
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<pre>#include <iostream> <br>#include <stdexcept> <br>using namespace std; <br> <br>int main() { <br> double *ptr; <br> <br> do { <br> try { <br> ptr = new double[1000000]; <br> } <br> catch(bad_alloc err) { <br> cout << "配置失败" <br> << err.what() <br> << endl; <br> return 1; <br> } <br> cout << "配置OK\n"; <br> } while(ptr); <br> <br> return 0;<br>}</pre>
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执行结果：</span><br>
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<td style="background-color: rgb(0, 0, 0);"><small><span style="color: rgb(255, 255, 255);">....<br>
配置OK <br>
配置OK <br>
配置OK <br>
配置OK <br>
配置OK <br>
配置OK <br>
配置OK <br>
配置失败St9bad_alloc</span></small><span style="color: rgb(255, 255, 255);"><br>
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