Linux I/O篇

Test1:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc,char *argv[])
{
        char buf[128];
        memset(buf,0x00,sizeof(buf));

        int len = read(STDIN_FILENO,buf,sizeof(buf));

        write(STDOUT_FILENO,buf,len);


        return 0;

}

Test2:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <string.h>
int main(int argc,char *argv[])
{
        if(argc < 3)
        {
                printf("inupt error!");//了解printf刷新缓冲的机制
                sleep(10);
                return 0;
        }

        int len;
        int fd_src,fd_dest;


        fd_src = open(argv[1],O_RDONLY);
        fd_dest = open(argv[2],O_CREAT|O_WRONLY|O_TRUNC,0777);
        char buf[1024];
        while(len = read(fd_src,buf,sizeof(buf)))
        {
                write(fd_dest,buf,len);
        }
        close(fd_src);
        close(fd_dest);
        printf("success!@!\n");

        return 0;
}

每一个文件流指针都对应着一个缓冲区指针，指向8192B的空间，这是为了提高读写效率，避免频繁的读写磁盘。

每次读写的内容都放在8192的缓冲区中，等待以下几个条件中的一个达到，刷新缓冲区。

刷新缓冲区的方法

1.     \n

2.     fflush

3.    缓冲区满

4.    程序正常退出

注：\n只能刷新终端文件缓冲区(stdin stdout stderr)

文件描述符的一些信息

lili@lili-linux:~$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 3823
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 3823
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

lili@lili-linux:~$ cat /proc/sys/fs/file-max
97384

lili@lili-linux:~$ cat /usr/include/asm-generic/errno-base.h
#ifndef _ASM_GENERIC_ERRNO_BASE_H
#define _ASM_GENERIC_ERRNO_BASE_H

#define EPERM            1      /* Operation not permitted */
#define ENOENT           2      /* No such file or directory */
#define ESRCH            3      /* No such process */
#define EINTR            4      /* Interrupted system call */
#define EIO              5      /* I/O error */
#define ENXIO            6      /* No such device or address */
#define E2BIG            7      /* Argument list too long */
#define ENOEXEC          8      /* Exec format error */
#define EBADF            9      /* Bad file number */
#define ECHILD          10      /* No child processes */
#define EAGAIN          11      /* Try again */
#define ENOMEM          12      /* Out of memory */
#define EACCES          13      /* Permission denied */
#define EFAULT          14      /* Bad address */
#define ENOTBLK         15      /* Block device required */
#define EBUSY           16      /* Device or resource busy */
#define EEXIST          17      /* File exists */
#define EXDEV           18      /* Cross-device link */
#define ENODEV          19      /* No such device */
#define ENOTDIR         20      /* Not a directory */
#define EISDIR          21      /* Is a directory */
#define EINVAL          22      /* Invalid argument */
#define ENFILE          23      /* File table overflow */
#define EMFILE          24      /* Too many open files */
#define ENOTTY          25      /* Not a typewriter */
#define ETXTBSY         26      /* Text file busy */
#define EFBIG           27      /* File too large */
#define ENOSPC          28      /* No space left on device */
#define ESPIPE          29      /* Illegal seek */
#define EROFS           30      /* Read-only file system */
#define EMLINK          31      /* Too many links */
#define EPIPE           32      /* Broken pipe */
#define EDOM            33      /* Math argument out of domain of func */
#define ERANGE          34      /* Math result not representable */