字符串操作函数的几个基本函数

//---------------------------------------------------------------------------
int strlen (const char *s)
{
    const char *sc;

    for (sc = s; *sc != '\0'; ++sc)
    {
    }
    return sc - s;
}

//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
int strcmp (const char *cs, const char *ct)
{
    signed char __res;

    while (1)
    {
        if ((__res = *cs - *ct++) != 0 || !*cs++)
            break;
    }
    return __res;
}

//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
int strncmp (const char *cs, const char *ct, int count)
{
    signed char __res = 0;

    while (count) 
    {
        //dbg_print("*cs = %c, *ct = %c, count = %d\n", *cs, *ct, count);
        if ((__res = *cs - *ct++) != 0 || !*cs++)
            break;
        count--;
    }
    return __res;
}

//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
void * memset (void *s, int c, int count)
{
    char *xs = s;

    while (count--)
        *xs++ = c;
    return s;
}

//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
void * memcpy (void *dest, const void *src, int count)
{
    char *tmp = dest;
    const char *s = src;

    while (count--)
        *tmp++ = *s++;
    return dest;
}

//---------------------------------------------------------------------------

//---------------------------------------------------------------------------
int memcmp (const void *cs, const void *ct, int 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;
}

//---------------------------------------------------------------------------

转载于:https://www.cnblogs.com/yuzaipiaofei/archive/2012/03/08/4124242.html