1、strcat 在lib/string.c中实现。
1 /**
2 * strcat - Append one %NUL-terminated string to another
3 * @dest: The string to be appended to
4 * @src: The string to append to it
5 */
6
7 char *strcat(char *dest, const char *src)
8 {
9 char *tmp = dest;
10
11 while (*dest)
12 dest++;
13 while ((*dest++ = *src++) != '\0')
14 ;
15 return tmp;
16 }
2、strcpy
在lib/string.c中实现。
1 /**
2 * strcpy - Copy a %NUL terminated string
3 * @dest: Where to copy the string to
4 * @src: Where to copy the string from
5 */
6 char *strcpy(char *dest, const char *src)
7 {
8 char *tmp = dest;
9
10 while ((*dest++ = *src++) != '\0')
11 /* nothing */;
12 return tmp;
13 }3、strcmp
在lib/string.c中实现。1 /** 2 * strcmp - Compare two strings 3 * @cs: One string 4 * @ct: Another string 5 */ 6 int strcmp(const char *cs, const char *ct) 7 { 8 unsigned char c1, c2; 9 10 while (1) {11 c1 = *cs++;12 c2 = *ct++;13 if (c1 != c2)14 return c1 < c2 ? -1 : 1;15 if (!c1)16 break;17 }18 return 0;19 }
4、strstr
在lib/string.c中实现。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 != '\0'; ++sc)10 /* nothing */;11 return sc - s;12 }13 /**14 * memcmp - Compare two areas of memory15 * @cs: One area of memory16 * @ct: Another area of memory17 * @count: The size of the area.18 */19 int memcmp(const void *cs, const void *ct, size_t count)20 {21 const unsigned char *su1, *su2;22 int res = 0;23 24 for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)25 if ((res = *su1 - *su2) != 0)26 break;27 return res;28 }29 /**30 * strstr - Find the first substring in a %NUL terminated string31 * @s1: The string to be searched32 * @s2: The string to search for33 */34 char *strstr(const char *s1, const char *s2)35 {36 size_t l1, l2;37 38 l2 = strlen(s2);39 if (!l2)40 return (char *)s1;41 l1 = strlen(s1);42 while (l1 >= l2) {43 l1--;44 if (!memcmp(s1, s2, l2))45 return (char *)s1;46 s1++;47 }48 return NULL;49 }5、strnstr6、memset在lib/string.c中实现。1 /** 2 * strnstr - Find the first substring in a length-limited string 3 * @s1: The string to be searched 4 * @s2: The string to search for 5 * @len: the maximum number of characters to search 6 */ 7 char *strnstr(const char *s1, const char *s2, size_t len) 8 { 9 size_t l2;10 11 l2 = strlen(s2);12 if (!l2)13 return (char *)s1;14 while (len >= l2) {15 len--;16 if (!memcmp(s1, s2, l2))17 return (char *)s1;18 s1++;19 }20 return NULL;21 }
在lib/string.c中实现。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 }7、memcpy
在lib/string.c中实现。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 }8、memmove
在lib/string.c中实现。关于memcpy和memmove的区别下面会进行分析。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 }
9、memchr
在lib/string.c中实现。1 /** 2 * memchr - Find a character in an area of memory. 3 * @s: The memory area 4 * @c: The byte to search for 5 * @n: The size of the area. 6 * 7 * returns the address of the first occurrence of @c, or %NULL 8 * if @c is not found 9 */10 void *memchr(const void *s, int c, size_t n)11 {12 const unsigned char *p = s;13 while (n-- != 0) {14 if ((unsigned char)c == *p++) {15 return (void *)(p - 1);16 }17 }18 return NULL;19 }
10、strsep
在lib/string.c中实现。1 /** 2 * strpbrk - Find the first occurrence of a set of characters 3 * @cs: The string to be searched 4 * @ct: The characters to search for 5 */ 6 char *strpbrk(const char *cs, const char *ct) 7 { 8 const char *sc1, *sc2; 9 10 for (sc1 = cs; *sc1 != '\0'; ++sc1) {11 for (sc2 = ct; *sc2 != '\0'; ++sc2) {12 if (*sc1 == *sc2)13 return (char *)sc1;14 }15 }16 return NULL;17 }18 19 /**20 * strsep - Split a string into tokens21 * @s: The string to be searched22 * @ct: The characters to search for23 *24 * strsep() updates @s to point after the token, ready for the next call.25 *26 * It returns empty tokens, too, behaving exactly like the libc function27 * of that name. In fact, it was stolen from glibc2 and de-fancy-fied.28 * Same semantics, slimmer shape. ;)29 */30 char *strsep(char **s, const char *ct)31 {32 char *sbegin = *s;33 char *end;34 35 if (sbegin == NULL)36 return NULL;37 38 end = strpbrk(sbegin, ct);39 if (end)40 *end++ = '\0';41 *s = end;42 return sbegin;43 }
【转载】memmove和memcopy的区别
memcpy和memmove（）都是C语言中的库函数，在头文件string.h中，作用是拷贝一定长度的内存的内容，原型分别如下：
void
*memcpy(void *dst, const void *src, size_t count);
void *memmove(void
*dst, const void *src, size_t count);
他们的作用是一样的，唯一的区别是，当内存发生局部重叠的时候，memmove保证拷贝的结果是正确的，memcpy不保证拷贝的结果的正确。
第一种情况下，拷贝重叠的区域不会出现问题，内容均可以正确的被拷贝。
第二种情况下，问题出现在右边的两个字节，这两个字节的原来的内容首先就被覆盖了，而且没有保存。所以接下来拷贝的时候，拷贝的是已经被覆盖的内容，显然这是有问题的。
实际上，memcpy只是memmove的一个子集。