string.c总结

ubuntuer

  今日终于得闲,不用读fucking algorithm,study shit data structure!!!那就看看string吧,其实string以前写过,奈何这种东东基本上不用时隔多久就会忘掉忘掉的!!!注明下我这里这个string.c是lib/string.c下的,
  stupid library routines.. The optimized versions should generally be found as inline code in !!!
  但是只有这个stupid library才是我所懂的,optimized versions全是汇编,想看自己去看了,在下是不会汇编的!!!

  抬头的这句话,让我汗颜..
  Fri Jun 25 1999, Ingo Oeser
  * -  Added strsep() which will replace strtok() soon (because strsep() is
  *    reentrant and should be faster). Use only strsep() in new code, please.
  知道国内的很多文章,书籍字符串分割都是用的strtok!!!!看看这个,1999年就说到是strsep就将替代strtok了,害的老子以前还分析strtok,BBS也还经常有人问strtok!!!还谈什么发展软件行业哦!!!

  用了下strsep却是比strtok好用!!!!
char   ptr[]={ "abcdefghijklmnopqrstuvwxyz "};
char   *p,*str= "m ";
p=ptr;
printf( "%s\n ",strsep(&p,str));
printf( "%s\n ",p);
str= "s ";
printf( "%s\n ",strsep(&p,str));
printf( "%s\n ",p);



/**
* strlcpy - Copy a %NUL terminated string into a sized buffer
* @dest: Where to copy the string to
* @src: Where to copy the string from
* @size: size of destination buffer
*
* Compatible with *BSD: the result is always a valid
* NUL-terminated string that fits in the buffer (unless,
* of course, the buffer size is zero). It does not pad
* out the result like strncpy() does.
*/
size_t strlcpy(char *dest, const char *src, size_t size)
{
    size_t ret = strlen(src);
    if (size) {
        size_t len = (ret >= size) ? size - 1 : ret;
        memcpy(dest, src, len);
        dest[len] = '\0';
    }
    return ret;
}
EXPORT_SYMBOL(strlcpy);
#endif
#ifndef __HAVE_ARCH_STRCAT
/**
* strcat - Append one %NUL-terminated string to another
* @dest: The string to be appended to
* @src: The string to append to it
*/
#undef strcat
char *strcat(char *dest, const char *src)
{
    char *tmp = dest;
    while (*dest)
        dest++;
    while ((*dest++ = *src++) != '\0')
        ;
    return tmp;
}
EXPORT_SYMBOL(strcat);
#endif
#ifndef __HAVE_ARCH_STRNCAT
/**
* strncat - Append a length-limited, %NUL-terminated string to another
* @dest: The string to be appended to
* @src: The string to append to it
* @count: The maximum numbers of bytes to copy
*
* Note that in contrast to strncpy, strncat ensures the result is
* terminated.
*/
char *strncat(char *dest, const char *src, size_t count)
{
    char *tmp = dest;
    if (count) {
        while (*dest)
            dest++;
        while ((*dest++ = *src++) != 0) {
            if (--count == 0) {
                *dest = '\0';
                break;
            }
        }
    }
    return tmp;
}
EXPORT_SYMBOL(strncat);
#endif
#ifndef __HAVE_ARCH_STRLCAT
/**
* strlcat - Append a length-limited, %NUL-terminated string to another
* @dest: The string to be appended to
* @src: The string to append to it
* @count: The size of the destination buffer.
*/
size_t strlcat(char *dest, const char *src, size_t count)
{
    size_t dsize = strlen(dest);
    size_t len = strlen(src);
    size_t res = dsize + len;
    /* This would be a bug */
    BUG_ON(dsize >= count);
    dest += dsize;
    count -= dsize;
    if (len >= count)
        len = count-1;
    memcpy(dest, src, len);
    dest[len] = 0;
    return res;
}
EXPORT_SYMBOL(strlcat);
#endif
#ifndef __HAVE_ARCH_STRCMP
/**
* strcmp - Compare two strings
* @cs: One string
* @ct: Another string
*/
#undef strcmp
int strcmp(const char *cs, const char *ct)
{
    signed char __res;
    while (1) {
        if ((__res = *cs - *ct++) != 0 || !*cs++)
            break;
    }
    return __res;
}
EXPORT_SYMBOL(strcmp);
#endif
#ifndef __HAVE_ARCH_STRNCMP
/**
* strncmp - Compare two length-limited strings
* @cs: One string
* @ct: Another string
* @count: The maximum number of bytes to compare
*/
int strncmp(const char *cs, const char *ct, size_t count)
{
    signed char __res = 0;
    while (count) {
        if ((__res = *cs - *ct++) != 0 || !*cs++)
            break;
        count--;
    }
    return __res;
}
EXPORT_SYMBOL(strncmp);
#endif
#ifndef __HAVE_ARCH_STRCHR
/**
* strchr - Find the first occurrence of a character in a string
* @s: The string to be searched
* @c: The character to search for
*/
char *strchr(const char *s, int c)
{
    for (; *s != (char)c; ++s)
        if (*s == '\0')
            return NULL;
    return (char *)s;
}
EXPORT_SYMBOL(strchr);
#endif
#ifndef __HAVE_ARCH_STRRCHR
/**
* strrchr - Find the last occurrence of a character in a string
* @s: The string to be searched
* @c: The character to search for
*/
char *strrchr(const char *s, int c)
{
       const char *p = s + strlen(s);
       do {
           if (*p == (char)c)
               return (char *)p;
       } while (--p >= s);
       return NULL;
}
EXPORT_SYMBOL(strrchr);
#endif
#ifndef __HAVE_ARCH_STRNCHR
/**
* strnchr - Find a character in a length limited string
* @s: The string to be searched
* @count: The number of characters to be searched
* @c: The character to search for
*/
char *strnchr(const char *s, size_t count, int c)
{
    for (; count-- && *s != '\0'; ++s)
        if (*s == (char)c)
            return (char *)s;
    return NULL;
}
EXPORT_SYMBOL(strnchr);
#endif
/**
* strstrip - Removes leading and trailing whitespace from @s.
* @s: The string to be stripped.
*
* Note that the first trailing whitespace is replaced with a %NUL-terminator
* in the given string @s. Returns a pointer to the first non-whitespace
* character in @s.
*/
char *strstrip(char *s)
{
    size_t size;
    char *end;
    size = strlen(s);
    if (!size)
        return s;
    end = s + size - 1;
    while (end != s && isspace(*end))
        end--;
    *(end + 1) = '\0';
    while (*s && isspace(*s))
        s++;
    return s;
}
EXPORT_SYMBOL(strstrip);
#ifndef __HAVE_ARCH_STRLEN
/**
* strlen - Find the length of a string
* @s: The string to be sized
*/
size_t strlen(const char *s)
{
    const char *sc;
    for (sc = s; *sc != '\0'; ++sc)
        /* nothing */;
    return sc - s;
}
EXPORT_SYMBOL(strlen);
#endif
#ifndef __HAVE_ARCH_STRNLEN
/**
* strnlen - Find the length of a length-limited string
* @s: The string to be sized
* @count: The maximum number of bytes to search
*/
size_t strnlen(const char *s, size_t count)
{
    const char *sc;
    for (sc = s; count-- && *sc != '\0'; ++sc)
        /* nothing */;
    return sc - s;
}
EXPORT_SYMBOL(strnlen);
#endif
#ifndef __HAVE_ARCH_STRSPN
/**
* strspn - Calculate the length of the initial substring of @s which only
*     contain letters in @accept
* @s: The string to be searched
* @accept: The string to search for
*/
size_t strspn(const char *s, const char *accept)
{
    const char *p;
    const char *a;
    size_t count = 0;
    for (p = s; *p != '\0'; ++p) {
        for (a = accept; *a != '\0'; ++a) {
            if (*p == *a)
                break;
        }
        if (*a == '\0')
            return count;
        ++count;
    }
    return count;
}
EXPORT_SYMBOL(strspn);
#endif
#ifndef __HAVE_ARCH_STRCSPN
/**
* strcspn - Calculate the length of the initial substring of @s which does
*     not contain letters in @reject
* @s: The string to be searched
* @reject: The string to avoid
*/
size_t strcspn(const char *s, const char *reject)
{
    const char *p;
    const char *r;
    size_t count = 0;
    for (p = s; *p != '\0'; ++p) {
        for (r = reject; *r != '\0'; ++r) {
            if (*p == *r)
                return count;
        }
        ++count;
    }
    return count;
}
EXPORT_SYMBOL(strcspn);
#endif
#ifndef __HAVE_ARCH_STRPBRK
/**
* strpbrk - Find the first occurrence of a set of characters
* @cs: The string to be searched
* @ct: The characters to search for
*/
char *strpbrk(const char *cs, const char *ct)
{
    const char *sc1, *sc2;
    for (sc1 = cs; *sc1 != '\0'; ++sc1) {
        for (sc2 = ct; *sc2 != '\0'; ++sc2) {
            if (*sc1 == *sc2)
                return (char *)sc1;
        }
    }
    return NULL;
}
EXPORT_SYMBOL(strpbrk);
#endif
#ifndef __HAVE_ARCH_STRSEP
/**
* strsep - Split a string into tokens
* @s: The string to be searched
* @ct: The characters to search for
*
* strsep() updates @s to point after the token, ready for the next call.
*
* It returns empty tokens, too, behaving exactly like the libc function
* of that name. In fact, it was stolen from glibc2 and de-fancy-fied.
* Same semantics, slimmer shape. ;)
*/
char *strsep(char **s, const char *ct)
{
    char *sbegin = *s;
    char *end;
    if (sbegin == NULL)
        return NULL;
    end = strpbrk(sbegin, ct);
    if (end)
        *end++ = '\0';
    *s = end;
    return sbegin;
}
EXPORT_SYMBOL(strsep);
#endif
#ifndef __HAVE_ARCH_MEMSET
/**
* memset - Fill a region of memory with the given value
* @s: Pointer to the start of the area.
* @c: The byte to fill the area with
* @count: The size of the area.
*
* Do not use memset() to access IO space, use memset_io() instead.
*/
void *memset(void *s, int c, size_t count)
{
    char *xs = s;
    while (count--)
        *xs++ = c;
    return s;
}
EXPORT_SYMBOL(memset);
#endif
#ifndef __HAVE_ARCH_MEMCPY
/**
* memcpy - Copy one area of memory to another
* @dest: Where to copy to
* @src: Where to copy from
* @count: The size of the area.
*
* You should not use this function to access IO space, use memcpy_toio()
* or memcpy_fromio() instead.
*/
void *memcpy(void *dest, const void *src, size_t count)
{
    char *tmp = dest;
    const char *s = src;
    while (count--)
        *tmp++ = *s++;
    return dest;
}
EXPORT_SYMBOL(memcpy);
#endif
#ifndef __HAVE_ARCH_MEMMOVE
/**
* memmove - Copy one area of memory to another
* @dest: Where to copy to
* @src: Where to copy from
* @count: The size of the area.
*
* Unlike memcpy(), memmove() copes with overlapping areas.
*/
void *memmove(void *dest, const void *src, size_t count)
{
    char *tmp;
    const char *s;
    if (dest = src) {
        tmp = dest;
        s = src;
        while (count--)
            *tmp++ = *s++;
    } else {
        tmp = dest;
        tmp += count;
        s = src;
        s += count;
        while (count--)
            *--tmp = *--s;
    }
    return dest;
}
EXPORT_SYMBOL(memmove);
#endif
#ifndef __HAVE_ARCH_MEMCMP
/**
* memcmp - Compare two areas of memory
* @cs: One area of memory
* @ct: Another area of memory
* @count: The size of the area.
*/
#undef memcmp
int memcmp(const void *cs, const void *ct, size_t count)
{
    const unsigned char *su1, *su2;
    int res = 0;
    for (su1 = cs, su2 = ct; 0  count; ++su1, ++su2, count--)
        if ((res = *su1 - *su2) != 0)
            break;
    return res;
}
EXPORT_SYMBOL(memcmp);
#endif
#ifndef __HAVE_ARCH_MEMSCAN
/**
* memscan - Find a character in an area of memory.
* @addr: The memory area
* @c: The byte to search for
* @size: The size of the area.
*
* returns the address of the first occurrence of @c, or 1 byte past
* the area if @c is not found
*/
void *memscan(void *addr, int c, size_t size)
{
    unsigned char *p = addr;
    while (size) {
        if (*p == c)
            return (void *)p;
        p++;
        size--;
    }
      return (void *)p;
}
EXPORT_SYMBOL(memscan);
#endif
#ifndef __HAVE_ARCH_STRSTR
/**
* strstr - Find the first substring in a %NUL terminated string
* @s1: The string to be searched
* @s2: The string to search for
*/
char *strstr(const char *s1, const char *s2)
{
    int l1, l2;
    l2 = strlen(s2);
    if (!l2)
        return (char *)s1;
    l1 = strlen(s1);
    while (l1 >= l2) {
        l1--;
        if (!memcmp(s1, s2, l2))
            return (char *)s1;
        s1++;
    }
    return NULL;
}
EXPORT_SYMBOL(strstr);
#endif
#ifndef __HAVE_ARCH_MEMCHR
/**
* memchr - Find a character in an area of memory.
* @s: The memory area
* @c: The byte to search for
* @n: The size of the area.
*
* returns the address of the first occurrence of @c, or %NULL
* if @c is not found
*/
void *memchr(const void *s, int c, size_t n)
{
    const unsigned char *p = s;
    while (n-- != 0) {
            if ((unsigned char)c == *p++) {
            return (void *)(p - 1);
        }
    }
    return NULL;
}
EXPORT_SYMBOL(memchr);
#endif

这个还是值得看看的,应付笔试,面试时候的string函数是完全没有问题的了!!!


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