思考：
replace图解：
程序完善：
DTString.h：
1 #ifndef DTSTRING_H
2 #define DTSTRING_H
3
4 #include "Object.h"
5
6 namespace DTLib
7 {
8
9 class String : Object
10 {
11 protected:
12 char* m_str;
13 int m_length;
14
15 void init(const char* s);
16 bool equal(const char* l, const char* r, int len) const;
17
18 static int* make_pmt(const char* p);
19 static int kmp(const char* s, const char* p);
20
21 public:
22 String();
23 String(char c);
24 String(const char* s);
25 String(const String& s);
26
27 int length() const;
28 const char* str() const;
29
30 bool startWith(const char* s) const;
31 bool startWith(const String& s) const;
32 bool endOf(const char* s) const;
33 bool endOf(const String& s) const;
34
35 String& insert(int i, const char* s);
36 String& insert(int i, const String& s);
37
38 String& trim();
39
40 int indexOf(const char* s) const;
41 int indexOf(const String& s) const;
42
43 String& remove(int i, int len); //删除指定下标，指定长度的子串
44 String& remove(const char* s);
45 String& remove(const String& s);
46
47 String& replace(const char* t, const char* s);
48 String& replace(const String& t, const char* s);
49 String& replace(const char* t, const String& s);
50 String& replace(const String& t, const String& s);
51
52 String sub(int i, int len) const;
53
54 char& operator [] (int i);
55 char operator [] (int i) const;
56
57 bool operator == (const String& s) const;
58 bool operator == (const char* s) const;
59
60 bool operator != (const String& s) const;
61 bool operator != (const char* s) const;
62
63 bool operator > (const String& s) const;
64 bool operator > (const char* s) const;
65
66 bool operator < (const String& s) const;
67 bool operator < (const char* s) const;
68
69 bool operator >= (const String& s) const;
70 bool operator >= (const char* s) const;
71
72 bool operator <= (const String& s) const;
73 bool operator <= (const char* s) const;
74
75 String operator + (const String& s) const;
76 String operator + (const char* s) const;
77 String& operator += (const String& s);
78 String& operator += (const char* s);
79
80 String operator - (const char* s) const;
81 String operator - (const String& s) const;
82 String& operator -= (const char* s);
83 String& operator -= (const String& s);
84
85 String& operator = (const String& s);
86 String& operator = (const char* s);
87 String& operator = (char c);
88
89 ~String();
90 };
91
92 }
93
94
95 #endif // DTSTRING_H
DTString.cpp：
1 #include <cstring>
2 #include <cstdlib>
3 #include "DTString.h"
4 #include "Exception.h"
5
6 using namespace std;
7
8 namespace DTLib
9 {
10
11 int* String::make_pmt(const char* p) // O(m)
12 {
13 int len = strlen(p);
14
15 int* ret = static_cast<int*>(malloc(sizeof(int) * len));
16
17 if( ret != NULL )
18 {
19 int ll = 0;
20
21 ret[0] = 0; // 第0个元素（长度为1的字符串）的ll值为0
22
23 for(int i = 1; i < len; i++)
24 {
25 //不成功的情况
26 while( (ll > 0) && (p[ll] != p[i]) )
27 {
28 ll = ret[ll];
29 }
30
31 // 假设最理想的情况成立
32 //在前一个ll值的基础行进行扩展，只需比对最后扩展的字符是否相等
33 //相等的话ll值加1，并写入到部分匹配表
34 if( p[ll] == p[i] )
35 {
36 ll++;
37 }
38
39 ret[i] = ll; // 将ll值写入匹配表
40
41 }
42 }
43
44 return ret;
45 }
46
47 int String::kmp(const char* s, const char* p) //O(m) + O(n) = O(m + n)
48 {
49 int ret = -1;
50
51 int sl = strlen(s);
52 int pl = strlen(p); //子串
53
54 int* pmt = make_pmt(p); //O(m)
55
56 if( (pmt != NULL) && (0 < pl) && (pl <= sl))
57 {
58 for( int i = 0,j = 0; i < sl; i++ )
59 {
60 while( (j > 0) && (s[i] != p[j]) ) // j小于等于0时要退出
61 {
62 j = pmt[j];
63 }
64
65 if( s[i] == p[j] )
66 {
67 j++;
68 }
69
70 if( j == pl ) // j的值如果最后就是子串的长度，意味着查找到了
71 {
72 ret = i + 1 - pl; // 匹配成功时i的值停在最后一个匹配的字符上
73 break;
74 }
75 }
76 }
77
78 free(pmt);
79
80 return ret;
81 }
82
83 void String::init(const char* s)
84 {
85 m_str = strdup(s);
86
87 if( m_str )
88 {
89 m_length = strlen(m_str);
90 }
91 else
92 {
93 THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create string object ...");
94 }
95 }
96
97 bool String::equal(const char* l, const char* r, int len) const
98 {
99 bool ret = true;
100
101 for(int i = 0; i < len && ret; i++)
102 {
103 ret = ret && (l[i] == r[i]);
104 }
105
106 return ret;
107 }
108
109 String::String()
110 {
111 init("");
112 }
113
114 String::String(const char* s)
115 {
116 init(s ? s : ""); //空指针就转换成空字符串
117 }
118
119 String::String(const String& s)
120 {
121 init(s.m_str);
122 }
123
124 String::String(char c)
125 {
126 char s[] = {c, ' '};
127
128 init(s);
129 }
130
131 int String::length() const
132 {
133 return m_length;
134 }
135
136 const char* String::str() const
137 {
138 return m_str;
139 }
140
141 bool String::startWith(const char* s) const
142 {
143 bool ret = ( s != NULL );
144
145 if( ret )
146 {
147 int len = strlen(s);
148
149 ret = (len < m_length) && equal(m_str, s, len);
150
151 }
152
153 return ret;
154 }
155
156 bool String::startWith(const String& s) const
157 {
158 return startWith(s.m_str);
159 }
160
161 bool String::endOf(const char* s) const
162 {
163 bool ret = ( s != NULL );
164
165 if( ret )
166 {
167 int len = strlen(s);
168
169 char* str = m_str + (m_length - len);
170
171 ret = (len < m_length) && equal(str, s, len);
172
173 }
174
175 return ret;
176 }
177
178 bool String::endOf(const String& s) const
179 {
180 return endOf(s.m_str);
181 }
182
183 String& String::insert(int i, const char* s)
184 {
185 if( (0 <= i) && (i <= m_length) )
186 {
187 if( ( s != NULL) && ( s[0] != ' ' ) )
188 {
189 int len = strlen(s);
190 char* str = reinterpret_cast<char*>(malloc(m_length + len + 1));
191
192 if( str != NULL )
193 {
194 strncpy(str, m_str, i);
195 strncpy(str + i, s, len);
196 strncpy(str + i + len, m_str + i, m_length - i);
197
198 str[m_length + len] = ' ';
199
200 free(m_str);
201
202 m_str = str;
203 m_length = m_length + len;
204 }
205 else
206 {
207 THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create str object...");
208 }
209 }
210 }
211 else
212 {
213 THROW_EXCEPTION(IndexOutOfBoundsException, "parameter i is invalid...");
214 }
215
216 return *this;
217 }
218
219 String& String::insert(int i, const String& s)
220 {
221 return insert(i, s.m_str);
222 }
223
224 String& String::trim()
225 {
226 int b = 0;
227 int e = m_length - 1;
228
229 while( m_str[b] == ' ')b++;
230 while( m_str[e] == ' ')e--;
231
232 if( b == 0 )
233 {
234 m_str[e + 1] = ' ';
235
236 m_length = e + 1;
237 }
238 else
239 {
240 for(int i = 0,j = b; j <= e; i++, j++)
241 {
242 m_str[i] = m_str[j];
243 }
244
245 m_str[e - b + 1] = ' ';
246 m_length = e - b + 1;
247 }
248
249 return *this;
250 }
251
252 int String::indexOf(const char* s) const
253 {
254 return kmp(m_str, s ? s : "");
255 }
256
257 int String::indexOf(const String& s) const
258 {
259 return kmp(m_str, s.m_str);
260 }
261
262 String& String::remove(int i, int len)
263 {
264 if( (0 <= i) && (i < m_length) )
265 {
266 int n = i;
267 int m = i + len;
268
269 while( (n < m) && (m < m_length) )
270 {
271 m_str[n++] = m_str[m++];
272 }
273
274 m_str[n] = ' ';
275 m_length = n;
276 }
277
278 return *this;
279 }
280
281 String& String::remove(const char* s)
282 {
283 return remove(indexOf(s), s ? strlen(s) : 0);
284 }
285
286 String& String::remove(const String& s)
287 {
288 return remove(indexOf(s), s.length());
289 }
290
291 String& String::replace(const char* t, const char* s)
292 {
293 int index = indexOf(t);
294
295 if( index >= 0 )
296 {
297 remove(t);
298 insert(index, s);
299 }
300
301 return *this;
302 }
303
304 String& String::replace(const String& t, const char* s)
305 {
306 return replace(t.m_str, s);
307 }
308
309 String& String::replace(const char* t, const String& s)
310 {
311 return replace(t, s.m_str);
312 }
313
314 String& String::replace(const String& t, const String& s)
315 {
316 return replace(t.m_str, s.m_str);
317 }
318
319 String String::sub(int i, int len) const
320 {
321 String ret;
322
323 if( (0 <= i) && (i<m_length) )
324 {
325 if( len < 0 ) len = 0;
326 if(len + i > m_length) len = m_length - i;
327
328 char* str = reinterpret_cast<char*>(malloc(len + 1));
329
330 strncpy(str, m_str + i, len);
331
332 str[len] = ' ';
333
334 ret = str;
335 }
336 else
337 {
338 THROW_EXCEPTION(IndexOutOfBoundsException, "parameter i is invalid...");
339 }
340
341 return ret;
342 }
343
344 char& String::operator [] (int i)
345 {
346 if( (0 <= i) && (i < m_length) )
347 {
348 return m_str[i];
349 }
350 else
351 {
352 THROW_EXCEPTION(IndexOutOfBoundsException, "parameter i is invalid ...");
353 }
354 }
355
356 char String::operator [] (int i) const
357 {
358 return (const_cast<String&>(*this))[i];
359 }
360
361 bool String::operator == (const String& s) const
362 {
363 return ( strcmp(m_str, s.m_str) == 0 );
364 }
365
366 bool String::operator == (const char* s) const
367 {
368 return ( strcmp(m_str, s ? s : "") == 0 );
369 }
370
371 bool String::operator != (const String& s) const
372 {
373 return !(*this == s);
374 }
375
376 bool String::operator != (const char* s) const
377 {
378 return !(*this == s);
379 }
380
381 bool String::operator > (const String& s) const
382 {
383 return (strcmp(m_str, s.m_str) > 0);
384 }
385
386 bool String::operator > (const char* s) const
387 {
388 return (strcmp(m_str, s ? s : "") > 0);
389 }
390
391 bool String::operator < (const String& s) const
392 {
393 return (strcmp(m_str, s.m_str) < 0);
394 }
395
396 bool String::operator < (const char* s) const
397 {
398 return (strcmp(m_str, s ? s : "") < 0);
399 }
400
401 bool String::operator >= (const String& s) const
402 {
403 return (strcmp(m_str, s.m_str) >= 0);
404 }
405
406 bool String::operator >= (const char* s) const
407 {
408 return (strcmp(m_str, s ? s : "") >= 0);
409 }
410
411 bool String::operator <= (const String& s) const
412 {
413 return (strcmp(m_str, s.m_str) <= 0);
414 }
415
416 bool String::operator <= (const char* s) const
417 {
418 return (strcmp(m_str, s ? s : "") <= 0);
419 }
420
421 String String::operator + (const String& s) const
422 {
423 return (*this + s.m_str);
424 }
425
426 String String::operator + (const char* s) const
427 {
428 String ret;
429
430 int len = m_length + strlen(s ? s : "");
431
432 char* str = reinterpret_cast<char*>(malloc(len + 1));
433
434 if( str )
435 {
436 strcpy(str, m_str);
437 strcat(str, s ? s : "");
438
439 free(ret.m_str);
440
441 ret.m_str = str;
442 ret.m_length = len;
443 }
444 else
445 {
446 THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create str object...");
447 }
448
449 return ret;
450 }
451
452 String& String::operator += (const String& s)
453 {
454 return (*this = *this + s.m_str);
455 }
456
457 String& String::operator += (const char* s)
458 {
459 return (*this = *this + s);
460 }
461
462 String String::operator - (const char* s) const
463 {
464 return String(*this).remove(s);
465 }
466
467 String String::operator - (const String& s) const
468 {
469 return String(*this).remove(s);
470 }
471
472 String& String::operator -= (const char* s)
473 {
474 return remove(s);
475 }
476
477 String& String::operator -= (const String& s)
478 {
479 return remove(s);
480 }
481
482 String& String::operator = (const String& s)
483 {
484 return (*this = s.m_str);
485 }
486
487 String& String::operator = (const char* s)
488 {
489 if( m_str != s )
490 {
491 char* str = strdup(s ? s: "");
492
493 if( str )
494 {
495 free(m_str);
496
497 m_str = str;
498 m_length = strlen(m_str);
499 }
500 else
501 {
502 THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create str object...");
503 }
504 }
505
506 return *this;
507 }
508
509 String& String::operator = (char c)
510 {
511 char s[] = {c, ' '};
512
513 return (*this = s);
514 }
515
516 String::~String()
517 {
518 free(m_str);
519 }
520
521 }
小结：
