C字符串操作函数实现

时间：2010-06-20 来源：violetjiao

#ifndef NULL
#define NULL ((void *)0)
#endif

/*
    memcpy的实现代码
*/
void* memcpy(void *pDst, void *pSrc, int iLen)
{
    char *pTmp = (char *)pDst;
    char *pTmp2 = (char *)pSrc;

    if(0 == iLen)
        return pDst;
    while(iLen--)
        *pTmp++ = *pTmp2++;
    return pDst;
}

/*
    memset的实现代码
*/
void* memset(void *pDst, int iSet, int iLen)
{
    char *pTmp = (char *)pDst;
    if(0 == iLen)
        return pDst;
    while(iLen--)
        *pTmp++ = (char)iSet;
    return pDst;
}

/*
    strcpy的实现代码
*/
char *strcpy(char *pDst, char *pSrc)
{
    char *pRst = pDst;
    do
        *pDst++ = *pSrc;
    while(*pSrc++);
    return pRst;
}

/*
    strcat的实现代码
*/
char *strcat(char *s, char *a)
{
    char *save = s;
    for(; *s; ++s);
    while((*s++ = *a++) != 0);
    return save;
}

/*
    strlen的实现代码
*/
int strlen(char *pStr)
{
    int iLen = 0;
    while(*pStr++)
        iLen++;
    return iLen;
}

/*
    strcmp的实现
*/
int strcmp(char *s, char *t)
{
    for(; *s == *t; s++, t++)
    {
        if(('\0' == *s) || ('\0' == *t))
        {
            if(*s == *t)
                return 0;
            else
                break;
        }
    }
    return ((*s > *t) ? 1 : -1);
}

/*
    strncmp的实现
*/
int m_strncmp(char *s, char *t, int n)
{
    if(0 == n)
        return 0;
    for (; (--n > 0) && (*s==*t); s++,t++)
    {
        if ('\0'==*s)
            return 0;
    }
    if(*s == *t)
        return 0;
    return ((*s > *t) ? 1 : -1);
}

/*
    strstr的实现
*/
char* strstr(char *s, char *find)
{
    char c, sc;
    unsigned int len;

    if ((c = *find++) != 0)
    {
        len = lzs_strlen(find);
        do
        {
            do
            {
                if ((sc = *s++) == 0)
                    return (NULL);
            } while (sc != c);
        } while (lzs_strncmp(s, find, len) != 0);
        s--;
    }
    return ((char *)s);
}

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