读取文本 若有重复行则不输出

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

int main()
{
FILE *fr=fopen("D:\\chengxu\\2.txt","r");
if(fr==NULL)
{
exit(-1);
}
char *buff=(char *)malloc(128);
char *str=(char *)malloc(128);
char *s=(char *)malloc(1024);
memset(s,0,1024);
assert(buff!=NULL);
assert(str!=NULL);
assert(s!=NULL);

while(fgets(buff,128,fr) != NULL)
{
if(strcmp(str,buff) != 0)
{
strcpy(str,buff);
strcat(s,str);//
}
}
//buff=NULL;

printf("%s\n",s);
fclose(fr);
free(buff);
free(str);
free(s);
return 0;
}