该C函数完成从后向前进行字符串的查找

#include
#include

/*
 function : get the position of keyword in a given string
 input : the original string , keyword of searching
 output : the position of keyword in given string
*/
int poslastkey(const char *str, const char *strkey)
{
 int iLen, ikeyLen;
 int iPos;
 
 if(str == NULL || strkey == NULL)
  return -1;//输入参数有误

 iLen = strlen(str);
 ikeyLen = strlen(strkey);
 iPos = (unsigned int)str + iLen - ikeyLen;
 
 //对字符串进行比较
 while(strncmp((char *)iPos, strkey, ikeyLen)!=0 && iPos >= (unsigned int)str)
   --iPos;
 
 if(iPos < (unsigned int)str)
  return -2; //在串中没有找到输入的关键字

 return (iPos - (unsigned int)str);
}
/*
 function : get the last string according the key word
 input : the original string , keyword of searching
 output : the word from the keyword to the end of string
*/
char* laststr(const char *str, const char *strkey)
{
 int ikeyLen;
 int iPos;
   
 if(str == NULL || strkey == NULL)
  return NULL;
 
 iPos = poslastkey(str, strkey);
 if(iPos < 0)
 {
  return NULL;
 }
 else
 {
  ikeyLen = strlen(strkey);
  iPos = (unsigned int)str + iPos + ikeyLen;
  
  return (char *)iPos;
 }
}

int main(int argc, char *argv[])
{
 printf("%s", laststr("12345", "5"));
 return 0;
}