实现strrstr，找到子串最后的出现位置

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>
char* taishan_strrstr(const char *pSrc, const char* pSub)
{
    assert(pSrc);
    assert(pSub);
    char* pLastFound = NULL;
    char* pTemp      = (char*)pSrc;
    int   nSubLen    = strlen(pSub);
    if(   pSrc == NULL || pSrc[0] == 0
       || pSub == NULL || pSub[0] == 0)
    {
        return NULL;
    }
    while (pTemp)
    {
        pTemp = strstr(pTemp, pSub);
        if (!pTemp)
        {
            break;
        }
        pLastFound  = pTemp;
        pTemp      += nSubLen;
    }
    return pLastFound;
}
int main()
{
    const char* pSrc   = "Taishan Office, Tai'an";
    const char* pSub   = "Tai";
          char* pRight = taishan_strrstr(pSrc, pSub);
    printf("right found=%s\n", pRight);
    return 0;
}