open、read write

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>

int main(int argc,char *argv[]){
        int fd = 0;
        //fd = open("../demo01/source/main.cpp",O_RDONLY);
        //fd = open("./test.c",O_WRONLY|O_CREAT|O_TRUNC,0644);//rw-r--r--
        fd = open(argv[1],O_RDONLY);
        int fdw;
        fdw= open(argv[2],O_WRONLY|O_CREAT|O_TRUNC,0644);

        if(-1 == fd){
                printf("open failed");
                printf("errno=%d,%s\n",errno,strerror(errno));

        }
        if(-1 == fdw){
                printf("open failed");
        }

//ssize_t read(int fd, void *buf, size_t count);
        ssize_t nread;
        char buff[1024];
        while((nread = read(fd,buff,20))!=0){
                write(fdw,buff,nread);
        }
        printf("%d,%d\n",fd,fdw);
        close(fd);
        close(fdw);
}