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In order to illustrate a problem with the setjmp library function, I created a v_string class. The test code for this function (minus the setjmp problem) is listed below.
Now I always try and code carefully to avoid errors and memory leaks. Yet this program failed because I was too careful. What's going on?
1 /************************************************
2 * Combine strings with a variable length *
3 * string class. *
4 *************************************************/
5 #include <iostream>
6 #include <cstring>
7
8 /************************************************
9 * v_string -- variable length C style string *
10 * *
11 * Member functions: *
12 * set -- set the value of the string. *
13 * get -- get the data from the string. *
14 ************************************************/
15 class v_string
16 {
17 public:
18 const char *data; // The data
19 // Default constructor
20 v_string(): data(NULL)
21 {}
22 v_string(const char *const i_data):
23 data(strdup(i_data))
24 {}
25 // Destructor
26 ~v_string(void)
27 {
28 // Note: delete works
29 // even if data is NULL
30 delete [] data;
31 data = NULL;
32 }
33 // Copy constructor
34 v_string(const v_string &old)
35 {
36 if (data != NULL)
37 {
38 delete[] data;
39 data = NULL;
40 }
41 data = strdup(old.data);
42 }
43 // operator =
44 v_string & operator = (
45 const v_string &old)
46 {
47 if (this == &old)
48 return (*this);
49
50 if (data != NULL)
51 {
52 delete[] data;
53 data = NULL;
54 }
55 if (old.data == NULL)
56 {
57 data = NULL;
58 return (*this);
59 }
60
61 data = strdup(old.data);
62 return (*this);
63 }
64 public:
65 // Set a value
66 void set(
67 // New string value
68 const char *const new_data
69 )
70 {
71 if (data != NULL)
72 {
73 delete [] data;
74 data = NULL;
75 }
76 data = strdup(new_data);
77
78 }
79 // Returns the value of the string
80 const char * const get(void) const
81 {
82 return (data);
83 }
84 };
85 /************************************************
86 * operator + -- Combine two v_strings *
87 ************************************************/
88 v_string operator + (
89 const v_string &first, // First string
90 const v_string &second // Second string
91 )
92 {
93 char tmp[100]; // Combined string
94
95 strcpy(tmp, first.get());
96 strcat(tmp, second.get());
97
98 // Strings put together
99 v_string together(tmp);
100 return (together);
101 }
102
103 /************************************************
104 * combine -- Combine two strings and *
105 * print the result. *
106 ************************************************/
107 static void combine(
108 const v_string &first, // First string
109 const v_string &second // Second string
110 )
111 {
112 v_string together; // Strings put together
113 together = first + second;
114
115 std::cout << "Combination " <<
116 together.get() << '\n';
117 }
118
119 int main()
120 {
121 // Strings to combine
122 v_string first("First:");
123 v_string second("Second");
124 combine(first, second);
125 return (0);
126 }
(Next Hint 65. Answer 115.)
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