mem

    mem 库函数系列用于内存处理。

/**
 * 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;
}

/**
 * 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;
}

/**
 * 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;
}

/**
 * memcmp - Compare two areas of memory
 * @cs: One area of memory
 * @ct: Another area of memory
 * @count: The size of the area.
 */

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;
}

/**
 * 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;
}

/**
 * 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;
}

注：摘自linux内核源码