Linux 应用程序 之 IO编程（一）

　　我的linux 环境是windows8.1 + VMware6.5.1+  Fedora14,参考书籍：第六章

      链接：Linux应用程序开发详解(1-11).pdf

 

我利用一个SSH软件SSH Secure File Transfer Client 来从Linux传输文件

来张虚拟机运行Fedora的图：

 

 

下面步入正题：

IO最基本操作：

 

//hello.c
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#define MAXSIZE
int main(void)
{
    int i,fd,size,len;
    char *buf ="hello! I'm wirting to this file!";
    char buf_r[10];
    len= strlen(buf);
    if((fd = open("/tmp/hello2.txt",O_CREAT |O_TRUNC | O_RDWR,0666))<0)//打开文件
    {
        perror("open:");
        exit(1);
    }else 
    {
     printf("open file :hello2.txt %d\n",fd);
    }    
    if((size =  write( fd, buf,len))<0)//写固定长度数据，buf
    {
        perror("write:");
        exit(1);
    }else
    {
        printf("Wirte %s size=%d\n",buf,size);
    }
    lseek(fd,0,SEEK_SET);//文件指针定位到文件头
    if((size = read(fd,buf_r,10))<0)//读10个字节的数据，这里没有考虑字符串最后一个字节为'\0',要完善
    {    
        perror("read:");
        exit(1);
    }else
    {
        printf("read from file:%s size=%d\n",buf_r,size);
           } 
        if( close(fd) < 0)//别忘记关闭
    {
        perror("Close:");
        exit(1);
    }else
    {
        printf("Close hello2.txt\n");
    }
    exit(0);
}

文件的访问涉及到进程间同步、互斥问题，采用Linux的fcntl(）函数来加锁。

//function lock_set 
void lock_set(int fd,int type)
{
    struct flock lock;
    lock.l_whence = SEEK_SET;
    lock.l_start = 0;
    lock.l_len = 0;
    while(1)
    {
        lock.l_type = type;
        if(fcntl(fd, F_SETLK,&lock) == 0) //如果要操作的文件已经加"写入锁"则fcntl（） 返回非0值
        {
            if(lock.l_type == F_RDLCK)
                printf("read lock set by %d\n",getpid());
            else if (lock.l_type == F_WRLCK)
                printf("write lock set by %d\n",getpid());
            else if (lock.l_type == F_UNLCK)
                printf("release lock by %d\n",getpid());
            return ;
        }
        fcntl(fd, F_GETLK,&lock);//上锁失败说明文件被锁住，则用"F_GETLK"来获取该锁的类型，包括上锁线程ID
        if(lock.l_type != F_UNLCK)
        {
            if(lock.l_type == F_RDLCK)
                printf("read lock already set by %d\n",
                    lock.l_pid);
            else if(lock.l_type == F_WRLCK)
                printf("write lock already set by %d\n",
                    lock.l_pid);
             getchar();
        }
    }
}

下面演示A进程给文件上"写入锁",然后B进程给文件上"读锁"的实验现象：
Souce Code  of A :

//hello3.c 即A 进程
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
//function lock_set 
//...
int main(void)
{
    int fd;
    fd=open("/tmp/hello3.txt",O_RDWR | O_CREAT,0666);
    if(fd < 0)
    {
        perror("open");
        exit(1);
    }
    //lock "write"
    lock_set(fd, F_WRLCK);//给"hello3.txt"文件上"写入锁"
    getchar();//等待，（按回车继续执行程序)
    //then unlock
    lock_set(fd,F_UNLCK);//去锁
    getchar(); 
    close(fd);
    exit(0);
}

Souce Code  of B:

//hello4.c   即B进程
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
//function lock_set 
//...
int main(void)
{
    int fd;
    fd=open("/tmp/hello3.txt",O_RDWR | O_CREAT,0666);
    if(fd < 0)
    {
        perror("open");
        exit(1);
    }
    //lock "read"
    lock_set(fd,F_RDLCK);//给我文件hello3.txt上"读锁"
    getchar();
    //then unlock
    lock_set(fd,F_UNLCK);
    getchar(); 
    close(fd);
    exit(0);
}

 

运行效果，

 Step1:运行A进程（./hello3）：

Step2:打开另一终端，运行B进程(./hello4):

Step3:A进程对应终端中按下回车键：

Step4:B进程终端中按下回车键：

OK，读写锁实验结束。

下面再了解下IO多路复用(用select)，这个对我来说有点难理解，贴上代码和效果图，以后斟酌。

//select.c
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
int main(void)
{
    int fds[2];
    char buf[7];
    int i,rc,maxfd;
    fd_set inset1,inset2;
    struct timeval tv;
    if((fds[0] = open("/tmp/hello5.txt",O_RDWR | O_CREAT,0666))<0)
        perror("open hello5");
    if((fds[1] = open("/tmp/hello50.txt",O_RDWR | O_CREAT,0666))<0)
        perror("open hello50");
    if((rc = write(fds[0],"hello!\n",7)))
        printf("rc=%d\n",rc);
    lseek(fds[0],0,SEEK_SET);
    maxfd = fds[0]>fds[1] ? fds[0] : fds[1];
    FD_ZERO(&inset1);
    FD_SET(fds[0],&inset1);
    FD_ZERO(&inset2);
    FD_SET(fds[1],&inset2);
    tv.tv_sec=2;
    tv.tv_usec=0;
    while(FD_ISSET(fds[0],&inset1) || FD_ISSET(fds[1],&inset2))
    {
        if(select(maxfd+1,&inset1,&inset2,NULL,&tv)<0)
            perror("select");
        else
         {
            if(FD_ISSET(fds[0],&inset1))
            {
                rc = read(fds[0],buf,7);
                if(rc>0)
                {
                 buf[rc]='\0';
                 printf("read %s\n",buf);
                }else
                 perror("read");
            }
            if(FD_ISSET(fds[1],&inset2))
            {
                rc = write(fds[1],buf,7);
                if(rc>0)
                {
                 buf[rc]='\0';
                 printf("rc=%d,write:%s\n",rc,buf);
                }else
                    perror("write");
                sleep(10);
            }
         }
    }
    exit(0);
}

效果图：

感谢您的阅读，boyang987 。转载请注明出处。