分析EOF究竟是什么

EOF仅仅是一种状态或者说条件，需要触发。read调用遇到文件结尾，触发该条件，结果将返回0。针对EOF，对于标准输入设备，普通文件，管道文件，网络套接字文件是read如何触发呢？下面程序将说明：

server.c 是socket套接字服务端，目的为了网络套接字文件是read如何触发测试用的。

###########################server.c##############################

#include <sys/socket.h>

#include <netinet/in.h>

#include <stdio.h>

int main()

{

int connfd;

struct sockaddr_in servadd;

int sockfd=socket(AF_INET, SOCK_STREAM, 0);

bzero(&servadd, sizeof(servadd));

servadd.sin_family=AF_INET;

servadd.sin_port=htons(9999);

servadd.sin_addr.s_addr=inet_addr("192.168.60.136");

socklen_t len = sizeof(servadd);

socklen_t Reuseaddr = 1;

setsockopt( sockfd, SOL_SOCKET, SO_REUSEADDR, &Reuseaddr, sizeof(Reuseaddr ) );

bind(sockfd, (const struct sockaddr *)&servadd, len);

listen(sockfd,8);

while( (connfd = accept(sockfd,(struct sockaddr *)&servadd, &len)) >0)

{

printf("##########################\n");

write(connfd,"abc",3);

}

return 0;

}

############################test.c############################

#include <stdio.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <netinet/in.h>

#include <strings.h>

#define MAXSIZE 256

#define FNAME "test"

int main()

{

char buf[MAXSIZE];

int ret,pipefd[2];

ret= read(0,buf,MAXSIZE);

printf("standart input ret:%d\n",ret);

int fd = open(FNAME,O_RDONLY|O_CREAT);

ret= read(fd,buf,1);

printf("regular file ret:%d\n",ret);

close(fd);

FILE *fp = fopen(FNAME, "r");

ret = fread(buf,1,1,fp);

printf("regular file ret:%d\n",ret);

fclose(fp);

pipe(pipefd);

close(pipefd[1]);

ret = read(pipefd[0],buf,1);

printf("pipe file ret:%d\n",ret);

int sockfd=socket(AF_INET, SOCK_STREAM, 0);

struct sockaddr_in servadd;

bzero(&servadd,sizeof(servadd));

servadd.sin_family = AF_INET;

servadd.sin_port = htons(9999);

servadd.sin_addr.s_addr=inet_addr("192.168.60.136");

connect(sockfd, (struct sockaddr *)&servadd, sizeof(servadd));

ret = read(sockfd,buf,3);

perror("err1");

ret = read(sockfd,buf,3);

printf("socket file ret2:%d\n",ret);

perror("err2");

}

测试过程：

1.运行下列命令

#gcc server.c -o server

#gcc test.c -o test

#./server

#./test

输入ctrl+d键
standart input ret:0

regular file ret:0

regular file ret:0

pipe file ret:0

socket file ret1:3

err1: Success

#killall server

触发socket EOF

socket file ret2:0

err2: Success

2.分析

#man read

RETURN VALUE

On success, the number of bytes read is returned (zero indicates end of file)

可见返回值为：0，已经触发了EOF，具体如何触发，参见程序.