combine error handler with virtual function.

practical_exercises/10_day_practice/day9/异常例子/9-2.cpp

@@ -0,0 +1,35 @@
+#include <iostream>
+using namespace std;
+class BasicException
+{
+public:
+    virtual string Where() { return "BasicException..."; }
+};
+class FileSysException : public BasicException
+{
+public:
+    virtual string Where() { return "FileSysException..."; }
+};
+class FileNotFound : public FileSysException
+{
+public:
+    virtual string Where() { return "FileNotFound..."; }
+};
+class DiskNotFound : public FileSysException
+{
+public:
+    virtual string Where() { return "DiskNotFound..."; }
+};
+int main()
+{
+    try
+    {
+        //        .....  //程序代码
+        DiskNotFound err;
+        throw &err;
+    }
+    catch (BasicException *p)
+    {
+        cout << p->Where() << endl;
+    }
+}