1: #ifndef INTARRAY_H
2: #define INTARRAY_H
3:
4: #include <assert.h> // for assert()
5:
6: class IntArray
7: {
8: private:
9: int m_nLength;
10: int *m_pnData;
11:
12: public:
13: IntArray()
14: {
15: m_nLength = 0;
16: m_pnData = 0;
17: }
18:
19: IntArray(int nLength)
20: {
21: m_pnData = new int[nLength];
22: m_nLength = nLength;
23: }
24:
25: ~IntArray()
26: {
27: delete[] m_pnData;
28: }
29:
30: void Erase()
31: {
32: delete[] m_pnData;
33: // We need to make sure we set m_pnData to 0 here, otherwise it will
34: // be left pointing at deallocated memory!
35: m_pnData = 0;
36: m_nLength = 0;
37: }
38:
39: int& operator[](int nIndex)
40: {
41: assert(nIndex >= 0 && nIndex < m_nLength);
42: return m_pnData[nIndex];
43: }
44:
45: // Reallocate resizes the array. Any existing elements will be destroyed.
46: // This function operates quickly.
47: void Reallocate(int nNewLength)
48: {
49: // First we delete any existing elements
50: Erase();
51:
52: // If our array is going to be empty now, return here
53: if (nNewLength<= 0)
54: return;
55:
56: // Then we have to allocate new elements
57: m_pnData = new int[nNewLength];
58: m_nLength = nNewLength;
59: }
60:
61: // Resize resizes the array. Any existing elements will be kept.
62: // This function operates slowly.
63: void Resize(int nNewLength)
64: {
65: // If we are resizing to an empty array, do that and return
66: if (nNewLength <= 0)
67: {
68: Erase();
69: return;
70: }
71:
72: // Now we can assume nNewLength is at least 1 element. This algorithm
73: // works as follows: First we are going to allocate a new array. Then we
74: // are going to copy elements from the existing array to the new array.
75: // Once that is done, we can destroy the old array, and make m_pnData
76: // point to the new array.
77:
78: // First we have to allocate a new array
79: int *pnData = new int[nNewLength];
80:
81: // Then we have to figure out how many elements to copy from the existing
82: // array to the new array. We want to copy as many elements as there are
83: // in the smaller of the two arrays.
84: if (m_nLength > 0)
85: {
86: int nElementsToCopy = (nNewLength > m_nLength) ? m_nLength : nNewLength;
87:
88: // Now copy the elements one by one
89: for (int nIndex=0; nIndex < nElementsToCopy; nIndex++)
90: pnData[nIndex] = m_pnData[nIndex];
91: }
92:
93: // Now we can delete the old array because we don't need it any more
94: delete[] m_pnData;
95:
96: // And use the new array instead! Note that this simply makes m_pnData point
97: // to the same address as the new array we dynamically allocated. Because
98: // pnData was dynamically allocated, it won't be destroyed when it goes out of scope.
99: m_pnData = pnData;
100: m_nLength = nNewLength;
101: }
102:
103: void InsertBefore(int nValue, int nIndex)
104: {
105: // Sanity check our nIndex value
106: assert(nIndex >= 0 && nIndex <= m_nLength);
107:
108: // First create a new array one element larger than the old array
109: int *pnData = new int[m_nLength+1];
110:
111: // Copy all of the elements up to the index
112: for (int nBefore=0; nBefore < nIndex; nBefore++)
113: pnData[nBefore] = m_pnData[nBefore];
114:
115: // insert our new element into the new array
116: pnData[nIndex] = nValue;
117:
118: // Copy all of the values after the inserted element
119: for (int nAfter=nIndex; nAfter < m_nLength; nAfter++)
120: pnData[nAfter+1] = m_pnData[nAfter];
121:
122: // Finally, delete the old array, and use the new array instead
123: delete[] m_pnData;
124: m_pnData = pnData;
125: m_nLength += 1;
126: }
127:
128: void Remove(int nIndex)
129: {
130: // Sanity check our nIndex value
131: assert(nIndex >= 0 && nIndex < m_nLength);
132:
133: // First create a new array one element smaller than the old array
134: int *pnData = new int[m_nLength-1];
135:
136: // Copy all of the elements up to the index
137: for (int nBefore=0; nBefore < nIndex; nBefore++)
138: pnData[nBefore] = m_pnData[nBefore];
139:
140: // Copy all of the values after the inserted element
141: for (int nAfter=nIndex+1; nAfter < m_nLength; nAfter++)
142: pnData[nAfter-1] = m_pnData[nAfter];
143:
144: // Finally, delete the old array, and use the new array instead
145: delete[] m_pnData;
146: m_pnData = pnData;
147: m_nLength -= 1;
148: }
149:
150: // A couple of additional functions just for convenience
151: void InsertAtBeginning(int nValue) { InsertBefore(nValue, 0); }
152: void InsertAtEnd(int nValue) { InsertBefore(nValue, m_nLength); }
153:
154: int GetLength() { return m_nLength; }
155: };
156:
157: #endif
158:
159: Now, let’s test it just to prove it works:
160: 1
161: 2
162: 3
163: 4
164: 5
165: 6
166: 7
167: 8
168: 9
169: 10
170: 11
171: 12
172: 13
173: 14
174: 15
175: 16
176: 17
177: 18
178: 19
179: 20
180: 21
181: 22
182: 23
183: 24
184: 25
185: 26
186: 27
187: 28
188: 29
189: 30www.2cto.com
190: 31
191: 32
192: 33
193:
194: #include <iostream>
195: #include "IntArray.h"
196:
197: using namespace std;
198:
199: int main()
200: {
201: // Declare an array with 10 elements
202: IntArray cArray(10);
203:
204: // Fill the array with numbers 1 through 10
205: for (int i=0; i<10; i++)
206: cArray[i] = i+1;
207:
208: // Resize the array to 8 elements
209: cArray.Resize(8);
210:
211: // Insert the number 20 before the 5th element
212: cArray.InsertBefore(20, 5);
213:
214: // Remove the 3rd element
215: cArray.Remove(3);
216:
217: // Add 30 and 40 to the end and beginning
218: cArray.InsertAtEnd(30);
219: cArray.InsertAtBeginning(40);
220:
221: // Print out all the numbers
222: for (int j=0; j<cArray.GetLength(); j++)
223: cout << cArray[j] << " ";
224:
225: return 0;
226: }
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