常用字符串函数汇总

「爱情、让人受尽委屈。」 2022-08-09 14:56 358阅读 0赞

1 /\*  
2   \*   linux/lib/string.c  
3   \*  
4   \*   Copyright (C) 1991, 1992   Linus Torvalds  
5   \*/  
6  
7 /\*  
8   \* stupid library routines.. The optimized versions should generally be found  
9   \* as inline code in <asm-xx/string.h>  
10   \*  
11   \* These are buggy as well..  
12   \*/  
13    
14 \#include <linux/types.h>  
15  
16 char \* \_\_\_strtok = NULL;  
17  
18 char \* strcpy(char \* dest,const char \*src)  
19 \{  
20          char \*tmp = dest;  
21  
22          while ((\*dest++ = \*src++) != '/0')  
23                  /\* nothing \*/;  
24          return tmp;  
25 \}  
26  
27 char \* strncpy(char \* dest,const char \*src,size\_t count)  
28 \{  
29          char \*tmp = dest;  
30  
31          while (count-- && (\*dest++ = \*src++) != '/0')  
32                  /\* nothing \*/;  
33  
34          return tmp;  
35 \}  
36  
37 char \* strcat(char \* dest, const char \* src)  
38 \{  
39          char \*tmp = dest;  
40  
41          while (\*dest)  
42                  dest++;  
43          while ((\*dest++ = \*src++) != '/0')  
44                  ;  
45  
46          return tmp;  
47 \}  
48  
49 char \* strncat(char \*dest, const char \*src, size\_t count)  
50 \{  
51          char \*tmp = dest;  
52  
53          if (count) \{  
54                  while (\*dest)  
55                          dest++;  
56                  while ((\*dest++ = \*src++)) \{  
57                          if (--count == 0)  
58                                  break;  
59                  \}  
60          \}  
61  
62          return tmp;  
63 \}  
64  
65 int strcmp(const char \* cs,const char \* ct)  
66 \{  
67          register signed char \_\_res;  
68  
69          while (1) \{  
70                  if ((\_\_res = \*cs - \*ct++) != 0 || !\*cs++)  
71                          break;  
72          \}  
73  
74          return \_\_res;  
75 \}  
76  
77 int strncmp(const char \* cs,const char \* ct,size\_t count)  
78 \{  
79          register signed char \_\_res = 0;  
80  
81          while (count) \{  
82                  if ((\_\_res = \*cs - \*ct++) != 0 || !\*cs++)  
83                          break;  
84                  count--;  
85          \}  
86  
87          return \_\_res;  
88 \}  
89  
90 char \* strchr(const char \* s,char c)  
91 \{  
92          for(; \*s != c; ++s)  
93                  if (\*s == '/0')  
94                          return NULL;  
95          return (char \*) s;  
96 \}  
97  
98 size\_t strlen(const char \* s)  
99 \{  
100          const char \*sc;  
101  
102          for (sc = s; \*sc != '/0'; ++sc)  
103                  /\* nothing \*/;  
104          return sc - s;  
105 \}  
106  
107 size\_t strnlen(const char \* s, size\_t count)  
108 \{  
109          const char \*sc;  
110  
111          for (sc = s; \*sc != '/0' && count--; ++sc)  
112                  /\* nothing \*/;  
113          return sc - s;  
114 \}  
115  
116 size\_t strspn(const char \*s, const char \*accept)  
117 \{  
118          const char \*p;  
119          const char \*a;  
120          size\_t count = 0;  
121  
122          for (p = s; \*p != '/0'; ++p) \{  
123                  for (a = accept; \*a != '/0'; ++a) \{  
124                          if (\*p == \*a)  
125                                  break;  
126                  \}  
127                  if (\*a == '/0')  
128                          return count;  
129                  ++count;  
130          \}  
131  
132          return count;  
133 \}  
134  
135 char \* strpbrk(const char \* cs,const char \* ct)  
136 \{  
137          const char \*sc1,\*sc2;  
138  
139          for( sc1 = cs; \*sc1 != '/0'; ++sc1) \{  
140                  for( sc2 = ct; \*sc2 != '/0'; ++sc2) \{  
141                          if (\*sc1 == \*sc2)  
142                                  return (char \*) sc1;  
143                  \}  
144          \}  
145          return NULL;  
146 \}  
147  
148 char \* strtok(char \* s,const char \* ct)  
149 \{  
150          char \*sbegin, \*send;  
151  
152          sbegin   = s ? s : \_\_\_strtok;  
153          if (!sbegin) \{  
154                  return NULL;  
155          \}  
156          sbegin += strspn(sbegin,ct);  
157          if (\*sbegin == '/0') \{  
158                  \_\_\_strtok = NULL;  
159                  return( NULL );  
160          \}  
161          send = strpbrk( sbegin, ct);  
162          if (send && \*send != '/0')  
163                  \*send++ = '/0';  
164          \_\_\_strtok = send;  
165          return (sbegin);  
166 \}  
167  
168 void \* memset(void \* s,char c,size\_t count)  
169 \{  
170          char \*xs = (char \*) s;  
171  
172          while (count--)  
173                  \*xs++ = c;  
174  
175          return s;  
176 \}  
177  
178 char \* bcopy(const char \* src, char \* dest, int count)  
179 \{  
180          char \*tmp = dest;  
181  
182          while (count--)  
183                  \*tmp++ = \*src++;  
184  
185          return dest;  
186 \}  
187  
188 void \* memcpy(void \* dest,const void \*src,size\_t count)  
189 \{  
190          char \*tmp = (char \*) dest, \*s = (char \*) src;  
191  
192          while (count--)  
193                  \*tmp++ = \*s++;  
194  
195          return dest;  
196 \}  
197  
198 void \* memmove(void \* dest,const void \*src,size\_t count)  
199 \{  
200          char \*tmp, \*s;  
201  
202          if (dest <= src) \{  
203                  tmp = (char \*) dest;  
204                  s = (char \*) src;  
205                  while (count--)  
206                          \*tmp++ = \*s++;  
207                  \}  
208          else \{  
209                  tmp = (char \*) dest + count;  
210                  s = (char \*) src + count;  
211                  while (count--)  
212                          \*--tmp = \*--s;  
213                  \}  
214  
215          return dest;  
216 \}  
217  
218 int memcmp(const void \* cs,const void \* ct,size\_t count)  
219 \{  
220          const unsigned char \*su1, \*su2;  
221          signed char res = 0;  
222  
223          for( su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)  
224                  if ((res = \*su1 - \*su2) != 0)  
225                          break;  
226          return res;  
227 \}  
228  
229 /\*  
230   \* find the first occurrence of byte 'c', or 1 past the area if none  
231   \*/  
232 void \* memscan(void \* addr, unsigned char c, size\_t size)  
233 \{  
234          unsigned char \* p = (unsigned char \*) addr;  
235  
236          while (size) \{  
237                  if (\*p == c)  
238                          return (void \*) p;  
239                  p++;  
240                  size--;  
241          \}  
242          return (void \*) p;  
243 \}