string函数库的原型

 1 #ifndef __HAVE_ARCH_STRCPY
 2 /**
 3  * strcpy - Copy a %NUL terminated string
 4  * @dest: Where to copy the string to
 5  * @src: Where to copy the string from
 6  */
 7 char *strcpy(char *dest, const char *src)
 8 {
 9         char *tmp = dest;
10 
11         while ((*dest++ = *src++) != '')
12                 /* nothing */;
13         return tmp;
14 }

char *strcpy

 1 /**
 2  * memcpy - Copy one area of memory to another
 3  * @dest: Where to copy to
 4  * @src: Where to copy from
 5  * @count: The size of the area.
 6  *
 7  * You should not use this function to access IO space, use memcpy_toio()
 8  * or memcpy_fromio() instead.
 9  */
10 void *memcpy(void *dest, const void *src, size_t count)
11 {
12         char *tmp = dest;
13         const char *s = src;
14 
15         while (count--)
16                 *tmp++ = *s++;
17         return dest;
18 }

void *memcpy

strcpy和memcpy主要有以下3方面的区别。
1、复制的内容不同。strcpy只能复制字符串，而memcpy可以复制任意内容，例如字符数组、整型、结构体、类等。
2、复制的方法不同。strcpy不需要指定长度，它遇到被复制字符的串结束符""才结束，所以容易溢出。memcpy则是根据其第3个参数决定复制的长度。
3、用途不同。通常在复制字符串时用strcpy，而需要复制其他类型数据时则一般用memcpy

 1 #ifndef __HAVE_ARCH_STRCMP
 2 /**
 3  * strcmp - Compare two strings
 4  * @cs: One string
 5  * @ct: Another string
 6  */
 7 
 8 int strcmp(const char *cs, const char *ct)
 9 {
10         unsigned char c1, c2;
11 
12         while (1) {
13                 c1 = *cs++;
14                 c2 = *ct++;
15                 if (c1 != c2)
16                         return c1 < c2 ? -1 : 1;
17                 if (!c1)
18                         break;
19         }
20         return 0;
21 }

int strcmp

 1 /**
 2  * strncmp - Compare two length-limited strings
 3  * @cs: One string
 4  * @ct: Another string
 5  * @count: The maximum number of bytes to compare
 6  */
 7 int strncmp(const char *cs, const char *ct, size_t count)
 8 {
 9         unsigned char c1, c2;
10 
11         while (count) {
12                 c1 = *cs++;
13                 c2 = *ct++;
14                 if (c1 != c2)
15                         return c1 < c2 ? -1 : 1;
16                 if (!c1)
17                         break;
18                 count--;
19         }
20         return 0;
21 }

int strncmp

 1 /**
 2  * strlen - Find the length of a string
 3  * @s: The string to be sized
 4  */
 5 size_t strlen(const char *s)
 6 {
 7         const char *sc;
 8 
 9         for (sc = s; *sc != ''; ++sc)
10                 /* nothing */;
11         return sc - s;
12 }

size_t strlen

 1 /**
 2  * memset - Fill a region of memory with the given value
 3  * @s: Pointer to the start of the area.
 4  * @c: The byte to fill the area with
 5  * @count: The size of the area.
 6  *
 7  * Do not use memset() to access IO space, use memset_io() instead.
 8  */
 9 void *memset(void *s, int c, size_t count)
10 {
11         char *xs = s;
12 
13         while (count--)
14                 *xs++ = c;
15         return s;
16 }

void *memset

 1 /**
 2  * memmove - Copy one area of memory to another
 3  * @dest: Where to copy to
 4  * @src: Where to copy from
 5  * @count: The size of the area.
 6  *
 7  * Unlike memcpy(), memmove() copes with overlapping areas.
 8  */
 9 void *memmove(void *dest, const void *src, size_t count)
10 {
11         char *tmp;
12         const char *s;
13 
14         if (dest <= src) {
15                 tmp = dest;
16                 s = src;
17                 while (count--)
18                         *tmp++ = *s++;
19         } else {
20                 tmp = dest;
21                 tmp += count;
22                 s = src;
23                 s += count;
24                 while (count--)
25                         *--tmp = *--s;
26         }
27         return dest;
28 }

void *memmove

 1 /**
 2  * memcmp - Compare two areas of memory
 3  * @cs: One area of memory
 4  * @ct: Another area of memory
 5  * @count: The size of the area.
 6  */
 7 int memcmp(const void *cs, const void *ct, size_t count)
 8 {
 9         const unsigned char *su1, *su2;
10         int res = 0;
11 
12         for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)
13                 if ((res = *su1 - *su2) != 0)
14                         break;
15         return res;
16 }

int memcmp