C语言编程:用命令行形式将一个文本文件的内容连接到另一个文本文件的末尾

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

int main(int argc,char * argv[])
{
int r,w;
char buf[1024];
FILE * s1,*s2,*d;
if(argc<4) {
printf("usage: name source1 source2 dest");
exit(255);
}

s1=fopen(argv[1],"rb");
s2=fopen(argv[2],"rb");
d=fopen(argv[3],"wb");

if(s1==NULL || s2==NULL || d==NULL) {
printf("error");
exit(255);
}
do {
r=fread(buf,1024,1,s1);
fwrite(buf,r,1,d);
} while(r==1024);

do {
r=fread(buf,1024,1,s2);
fwrite(buf,r,1,d);
} while(r==1024);

fclose(s1);
fclose(s2);
fclose(d);
}