#include<stdio.h>
#include<string.h>

void main()
{
char * temp;
char * tokenPtr;
char string[]="this is a sentence which 7 tokens";

tokenPtr=strtok(string," ");
temp=tokenPtr;

while(tokenPtr!=NULL)
{
tokenPtr=strtok(NULL," ");

if(strlen(temp)<strlen(tokenPtr)&&tokenPtr!=NULL)//最后一次执行while的时候，tokenPtr等于NULL,这里
temp=tokenPtr; //就是非法操作了

}
printf("the longest word is:%s\n",temp);
}