chap19.lst

< C++ 参考大全>>的源代码. 希望大家用得开心。

listing 1
// A simple exception handling example.
#include <iostream>
using namespace std;

int main()
{
  cout << "Start\n";

  try { // start a try block
    cout << "Inside try block\n";
    throw 100; // throw an error
    cout << "This will not execute";
  }
  catch (int i) { // catch an error
    cout << "Caught an exception -- value is: ";
    cout << i << "\n";
  }

  cout << "End";

  return 0;
}

listing 2
// This example will not work.
#include <iostream>
using namespace std;

int main()
{
  cout << "Start\n";

  try { // start a try block
    cout << "Inside try block\n";
    throw 100; // throw an error
    cout << "This will not execute";
  }
  catch (double i) { // won't work for an int exception
    cout << "Caught an exception -- value is: ";
    cout << i << "\n";
  }

  cout << "End";

  return 0;
}

listing 3
/* Throwing an exception from a function outside the
   try block. 
*/
#include <iostream>
using namespace std;

void Xtest(int test)
{
  cout << "Inside Xtest, test is: " << test << "\n";
  if(test) throw test;
}

int main()
{
  cout << "Start\n";

  try { // start a try block
    cout << "Inside try block\n";
    Xtest(0);
    Xtest(1);
    Xtest(2);
  }
  catch (int i) { // catch an error
    cout << "Caught an exception -- value is: ";
    cout << i << "\n";
  }

  cout << "End";

  return 0;
}

listing 4
#include <iostream>
using namespace std;

// Localize a try/catch to a function.
void Xhandler(int test)
{
  try{
    if(test) throw test;
  }
  catch(int i) {
    cout << "Caught Exception #: " << i << '\n';
  }
}

int main()
{
  cout << "Start\n";

  Xhandler(1);
  Xhandler(2);
  Xhandler(0);
  Xhandler(3);

  cout << "End";

  return 0;
}


listing 5
#include <iostream>
using namespace std;

int main()
{
  cout << "Start\n";

  try { // start a try block
    cout << "Inside try block\n";
    cout << "Still inside try block\n";
  }
  catch (int i) { // catch an error
    cout << "Caught an exception -- value is: ";
    cout << i << "\n";
  }

  cout << "End";

  return 0;
}

listing 6
// Catching class type exceptions.
#include <iostream>
#include <cstring>
using namespace std;

class MyException {
public:
  char str_what[80];
  int what;

  MyException() { *str_what = 0; what = 0; }

  MyException(char *s, int e) {
    strcpy(str_what, s);
    what = e;
  }
};

int main()
{
  int i;

  try {
    cout << "Enter a positive number: ";
    cin >> i;
    if(i<0)
      throw MyException("Not Positive", i); 
  }
  catch (MyException e) { // catch an error
    cout << e.str_what << ": ";
    cout << e.what << "\n";
  }

  return 0;
}


listing 7
#include <iostream>
using namespace std;

// Different types of exceptions can be caught.
void Xhandler(int test)
{
  try{
    if(test) throw test;
    else throw "Value is zero";
  }
  catch(int i) {
    cout << "Caught Exception #: " << i << '\n';
  }
  catch(const char *str) {
    cout << "Caught a string: ";
    cout << str << '\n';
  }
}

int main()
{
  cout << "Start\n";

  Xhandler(1);
  Xhandler(2);
  Xhandler(0);
  Xhandler(3);

  cout << "End";

  return 0;
}

listing 8
// Catching derived classes.
#include <iostream>
using namespace std;

class B {
};

class D: public B {
};

int main()
{
  D derived;

  try {
    throw derived;
  }
  catch(B b) {
    cout << "Caught a base class.\n";
  }
  catch(D d) {
    cout << "This won't execute.\n";
  }

  return 0;
}

listing 9
// This example catches all exceptions.
#include <iostream>
using namespace std;

void Xhandler(int test)
{
  try{
    if(test==0) throw test; // throw int
    if(test==1) throw 'a'; // throw char
    if(test==2) throw 123.23; // throw double
  }
  catch(...) { // catch all exceptions
    cout << "Caught One!\n";
  }
}

int main()
{
  cout << "Start\n";

  Xhandler(0);
  Xhandler(1);
  Xhandler(2);

  cout << "End";

  return 0;
}


listing 10
// This example uses catch(...) as a default.
#include <iostream>
using namespace std;

void Xhandler(int test)
{
  try{
    if(test==0) throw test; // throw int
    if(test==1) throw 'a'; // throw char
    if(test==2) throw 123.23; // throw double
  }
  catch(int i) { // catch an int exception
    cout << "Caught an integer\n";
  }
  catch(...) { // catch all other exceptions
    cout << "Caught One!\n";
  }
}

int main()
{
  cout << "Start\n";

  Xhandler(0);
  Xhandler(1);
  Xhandler(2);

  cout << "End";

  return 0;
}


listing 11
// Restricting function throw types.
#include <iostream>
using namespace std;

// This function can only throw ints, chars, and doubles.
void Xhandler(int test) throw(int, char, double)
{
  if(test==0) throw test; // throw int
  if(test==1) throw 'a'; // throw char
  if(test==2) throw 123.23; // throw double
}

int main()
{
  cout << "start\n";

  try{
    Xhandler(0); // also, try passing 1 and 2 to Xhandler()
  }
  catch(int i) {
    cout << "Caught an integer\n";
  }
  catch(char c) { 
    cout << "Caught char\n";
  }
  catch(double d) { 
    cout << "Caught double\n";
  }

  cout << "end";

  return 0;
}

listing 12
// This function can throw NO exceptions!
void Xhandler(int test) throw()
{
  /* The following statements no longer work.  Instead,
     they will cause an abnormal program termination. */
  if(test==0) throw test; 
  if(test==1) throw 'a'; 
  if(test==2) throw 123.23; 
}


listing 13
// Example of "rethrowing" an exception.
#include <iostream>
using namespace std;

void Xhandler()
{
  try {
    throw "hello"; // throw a char *
  }
  catch(const char *) { // catch a char *
    cout << "Caught char * inside Xhandler\n";
    throw ; // rethrow char * out of function
  }
}

int main()
{
  cout << "Start\n";

  try{
    Xhandler();
  }
  catch(const char *) {
    cout << "Caught char * inside main\n";
  }

  cout << "End";

  return 0;
}

listing 14
// Set a new terminate handler.
#include <iostream>
#include <cstdlib>
#include <exception>
using namespace std;

void my_Thandler() {
  cout << "Inside new terminate handler\n";
  abort();
}

int main()
{
  // set a new terminate handler
  set_terminate(my_Thandler);

  try { 
    cout << "Inside try block\n";
    throw 100; // throw an error
  }
  catch (double i) { // won't catch an int exception
    // ...
  }

  return 0;
}

listing 15
#include <iostream>
using namespace std;

void divide(double a, double b);

int main()
{
  double i, j;

  do {
    cout << "Enter numerator (0 to stop): ";
    cin >> i;
    cout << "Enter denominator: ";
    cin >> j;
    divide(i, j);
  } while(i != 0);

  return 0;
}

void divide(double a, double b)
{
  try {
    if(!b) throw b; // check for divide-by-zero   
    cout << "Result: " << a/b << endl;
  }
  catch (double b) {
    cout << "Can't divide by zero.\n";
  }
}