Lesson of 24 February 2011 (part B)

Using exceptions

An example of using exceptions

File exception1.cc

 1#include <iostream>
 2#include <cmath>
 3#include <string>
 4#include <sstream>
 5#include <stdexcept>
 6
 7using namespace std ;
 8
 9/*
10 * A simple example of exception handling
11 * 
12 */
13 
14class my_throw {
15public:
16  string where ;
17  my_throw( string const & file, unsigned line ) {
18    stringstream msg ;
19    msg << "Found an error in file: " << file << " at line: " << line ;
20    where = msg . str() ;
21  }
22} ;
23 
24#define MY_THROW throw my_throw( __FILE__, __LINE__ )
25
26// declare prototype
27void a() ;
28void b() ;
29void c() ;
30
31void
32a() {
33  cout << "Enter in routine a\n" ;
34  b() ;
35  cout << "Exit from routine a\n" ;
36} ;
37
38void
39b() {
40  cout << "Enter in routine b\n" ;
41  c() ;
42  cout << "Exit from routine b\n" ;
43} ;
44
45void
46c() {
47  cout << "Enter in routine c\n" ;
48  // make an exception
49  throw logic_error("pluto") ;
50  throw runtime_error("pippo") ;
51  MY_THROW ;
52  throw "I am and excption string" ;
53  cout << "Exit from routine c\n" ;
54} ;
55
56int
57main() {
58  try {
59    try {
60      a() ;
61    }
62    catch (...) {
63      cout << "nested exception\n" ;
64      throw ; // I rethrow the same exception to the upper block
65    }
66    a() ;
67  } 
68  catch ( int e ) {
69    cout << "found an exception!\n" ; 
70    cout << "value = " << e << "\n" ; 
71  }
72  catch ( char const str [] ) {
73    cout << "found an exception!\n" ; 
74    cout << "string = " << str << "\n" ; 
75  }
76  catch ( my_throw const & e ) {
77    cout << e . where << '\n' ;
78  }
79  catch ( runtime_error const & e ) {
80    cout << "runtime_error: " << e . what() << '\n' ;
81  }
82  catch ( exception const & e ) {
83    cout << "exception: " << e . what() << '\n' ;
84  }
85  catch ( ... ) {
86    cout << "found an exception!\n" ;
87  }
88  return 0 ;
89}

A second example

File exception2.cc

 1#include <iostream>
 2#include <cmath>
 3#include <string>
 4#include <sstream>
 5#include <stdexcept>
 6#include <memory>
 7
 8using namespace std ;
 9
10/*
11 * A simple stupid class
12 */
13
14class stupid {
15  string my_name ;
16public:
17  stupid( char const * n ) : my_name(n) {
18    cout << "contruct stupid(\"" << my_name << "\")\n" ;
19  }
20  ~stupid() {
21    cout << "destroy stupid(\"" << my_name << "\")\n" ;  
22  }
23} ;
24
25// declare prototype
26void a() ;
27void b() ;
28void c() ;
29
30long nw = 1ul<<30 ;
31
32void
33a() {
34  cout << "Enter in routine a\n" ;
35  stupid sa("sa") ;
36  auto_ptr<char> ptr(new char[nw]) ;
37  for ( long i = 0 ; i < nw ; i += 100 ) ptr.get()[i] = i % 234 ;
38  cout << "go ?" ; int a ; cin >> a ;
39  b() ;
40  cout << "Exit from routine a\n" ;
41} ;
42
43void
44b() {
45  cout << "Enter in routine b\n" ;
46  stupid sb("sb") ;
47  auto_ptr<char> ptr(new char[nw]) ;
48  for ( long i = 0 ; i < nw ; i += 100 ) ptr.get()[i] = i % 234 ;
49  cout << "go ?" ; int a ; cin >> a ;
50  c() ;
51  cout << "Exit from routine b\n" ;
52} ;
53
54void
55c() {
56  cout << "Enter in routine c\n" ;
57  stupid sc("sc") ;
58  auto_ptr<char> ptr(new char[nw]) ;
59  for ( long i = 0 ; i < nw ; i += 100 ) ptr.get()[i] = i % 234 ;
60  cout << "go ?" ; int a ; cin >> a ;
61  // make an exception
62  throw runtime_error("pippo") ;
63  cout << "Exit from routine c\n" ;
64} ;
65
66int
67main() {
68  try {
69    a() ;
70  } 
71  catch ( exception const & e ) {
72    cout << "exception: " << e . what() << '\n' ;
73  }
74  catch ( ... ) {
75    cout << "found an exception!\n" ;
76  }
77  cout << "finito ?" ;
78  int a ; cin >> a ;
79  return 0 ;
80}