strcpy函数在android中的实现

谁借莪１个温暖的怀抱￠ 2023-10-17 10:49 12阅读 0赞

一. 头文件声明：  
string.h:

\#ifndef \_STRING\_H\_  
\#define \_STRING\_H\_

\#include <sys/cdefs.h>  
\#include <stddef.h>  
\#include <malloc.h>

extern char\* strcpy(char \*, const char \*);  
extern char\* strcat(char \*, const char \*);  
......

\#endif /\* \_STRING\_H\_ \*/

二.函数实现：

1. strcat  
\#include <string.h>  
char \*strcat(char \*s, const char \*append)  
\{  
char \*save = s;

for (; \*s; ++s);  
while ((\*s++ = \*append++) != '/0');  
return(save);  
\}

2. strcpy  
\#include <string.h>

char \*strcpy(char \*to, const char \*from)  
\{  
char \*save = to;

for (; (\*to = \*from) != '/0'; ++from, ++to);  
return(save);  
\}

3. strlen  
size\_t strlen(const char \*str)  
\{  
const char \*s;

for (s = str; \*s; ++s)  
;  
return (s - str);  
\}

4. strcmp  
int strcmp(const char \*s1, const char \*s2)  
\{  
while (\*s1 == \*s2++)  
if (\*s1++ == 0)  
return (0);  
return (\*(unsigned char \*)s1 - \*(unsigned char \*)--s2);  
\}

5. strstr  
char \*strstr(const char \*s, const char \*find)  
\{  
char c, sc;  
size\_t len;

if ((c = \*find++) != 0) \{  
len = strlen(find);  
do \{  
do \{  
if ((sc = \*s++) == 0)  
return (NULL);  
\} while (sc != c);  
\} while (strncmp(s, find, len) != 0);  
s--;  
\}  
return ((char \*)s);  
\}

6. strncpy  
char \*strncpy(char \*dst, const char \*src, size\_t n)  
\{  
if (n != 0) \{  
char \*d = dst;  
const char \*s = src;

do \{  
if ((\*d++ = \*s++) == 0) \{  
/\* NUL pad the remaining n-1 bytes \*/  
while (--n != 0)  
\*d++ = 0;  
break;  
\}  
\} while (--n != 0);  
\}  
return (dst);  
\}

7. strncmp  
int strncmp(const char \*s1, const char \*s2, size\_t n)  
\{

if (n == 0)  
return (0);  
do \{  
if (\*s1 != \*s2++)  
return (\*(unsigned char \*)s1 - \*(unsigned char \*)--s2);  
if (\*s1++ == 0)  
break;  
\} while (--n != 0);  
return (0);  
\}

8. strncat  
char \*strncat(char \*dst, const char \*src, size\_t n)  
\{  
if (n != 0) \{  
char \*d = dst;  
const char \*s = src;

while (\*d != 0)  
d++;  
do \{  
if ((\*d = \*s++) == 0)  
break;  
d++;  
\} while (--n != 0);  
\*d = 0;  
\}  
return (dst);  
\}