**
系统调用函数
**
open系列系统调用-creat
**
int creat(const char* pathname,mode_t mode)
**
例题：在/home/dhh/c.d目录下创建一个tttt.txt文件
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
void main()
{
int fd=creat("/home/dhh/c.d/tttt.txt",0755);
if(fd==-1)
{
printf("errno:%d\n",errno);
}
else
{
printf("fd:%d,create file successful! ",fd);
}
}
注：0755->即表示用户具有读/写/执行（rwx）权限，组用户和其它用户具有读/执行（r-x）权限。
在程序运行前先ll查看c.d目录下的文件，没有tttt.txt
运行程序，成功，输出create file successful!
再次ll查看c.d目录，tttt.txt已被创建
**
int open(const char* pathname,int flags,mode_t mode)
**
mode_t指的是创建文件权限，比如上面说用到的0775。
flags是指打开文件的方式，一般是文件已经存在，用何种方式打开，一般主要有以下几种方式：
open函数其核心代码为：
int fd=open("/home/dhh/c.d/tttt.txt",O_RDWR|O_CREAT|O_EXCL,0755);
int close(int fd)
注：fd为文件操作符
当我们完成文件操作需要关闭文件，就要用到close函数
例题：打开一个文件然后关闭它
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
void main()
{
int state,fd;
fd=open("/home/dhh/c.d/tttt.txt",O_RDWR|O_CREAT,0755);
if(fd==-1)
{
printf("errno:%d,errno:%s\n",errno,strerror(errno));
exit(EXIT_FAILURE);
}
else
{
printf("fd:%d,open file successful!\n ",fd);
}
state=close(fd);
if(state==0)
{
printf("close file successful!\n");
}
else if(state==-1)
{
printf("errno:%d,errno:%s\n",errno,strerror(errno));
exit(EXIT_FAILURE);
}
}
说明文件被成功打开或关闭，若是出现错误无法打开则可以显示错误的代码和它所对应的错误描述。
Linux系统内核代码中errno的值及其对应的中文意思
/usr/include/asm/errno.h
#define EPERM 1 /* Operation not permitted */操作不允许
#define ENOENT 2 /* No such file or directory */文件/路径不存在
#define ESRCH 3 /* No such process */进程不存在
#define EINTR 4 /* Interrupted system call */中断的系统调用
#define EIO 5 /* I/O error */I/O错误
#define ENXIO 6 /* No such device or address */设备/地址不存在
#define E2BIG 7 /* Arg list too long */参数列表过长
#define ENOEXEC 8 /* Exec format error */执行格式错误
#define EBADF 9 /* Bad file number */错误文件编号
#define ECHILD 10 /* No child processes */子进程不存在
#define EAGAIN 11 /* Try again */重试
#define ENOMEM 12 /* Out of memory */内存不足
#define EACCES 13 /* Permission denied */无权限
#define EFAULT 14 /* Bad address */地址错误
#define ENOTBLK 15 /* Block device required */需要块设备
#define EBUSY 16 /* Device or resource busy */设备或资源忙
#define EEXIST 17 /* File exists */文件已存在
#define EXDEV 18 /* Cross-device link */跨设备链路
#define ENODEV 19 /* No such device */设备不存在
#define ENOTDIR 20 /* Not a directory */路径不存在
#define EISDIR 21 /* Is a directory */是路径
#define EINVAL 22 /* Invalid argument */无效参数
#define ENFILE 23 /* File table overflow */文件表溢出
#define EMFILE 24 /* Too many open files */打开的文件过多
#define ENOTTY 25 /* Not a typewriter */非打字机
#define ETXTBSY 26 /* Text file busy */文本文件忙
#define EFBIG 27 /* File too large */文件太大
#define ENOSPC 28 /* No space left on device */设备无空间
#define ESPIPE 29 /* Illegal seek */非法查询
#define EROFS 30 /* Read-only file system */只读文件系统
#define EMLINK 31 /* Too many links */链接太多
#define EPIPE 32 /* Broken pipe */管道破裂
#define EDOM 33 /* Math argument out of domain of func */参数超出函数域
#define ERANGE 34 /* Math result not representable */结果无法表示
#define EDEADLK 35 /* Resource deadlock would occur */资源将发生死锁
#define ENAMETOOLONG 36 /* File name too long */文件名太长
#define ENOLCK 37 /* No record locks available */没有可用的记录锁
#define ENOSYS 38 /* Function not implemented */函数未实现
#define ENOTEMPTY 39 /* Directory not empty */目录非空
#define ELOOP 40 /* Too many symbolic links encountered */遇到太多符号链接
#define EWOULDBLOCK EAGAIN /* Operation would block */操作会阻塞
#define ENOMSG 42 /* No message of desired type */没有符合需求类型的消息
#define EIDRM 43 /* Identifier removed */标识符已删除
#define ECHRNG 44 /* Channel number out of range */通道编号超出范围
#define EL2NSYNC 45 /* Level 2 not synchronized */level2不同步
#define EL3HLT 46 /* Level 3 halted */3级停止
#define EL3RST 47 /* Level 3 reset */3级重置
#define ELNRNG 48 /* Link number out of range */链接编号超出范围
#define EUNATCH 49 /* Protocol driver not attached */协议驱动程序没有连接
#define ENOCSI 50 /* No CSI structure available */没有可用的CSI结构
#define EL2HLT 51 /* Level 2 halted */2级停止
#define EBADE 52 /* Invalid exchange */无效交换
#define EBADR 53 /* Invalid request descriptor */无效请求描述
#define EXFULL 54 /* Exchange full */交换完全
#define ENOANO 55 /* No anode */无阳极
#define EBADRQC 56 /* Invalid request code */无效请求码
#define EBADSLT 57 /* Invalid slot */无效插槽
#define EDEADLOCK EDEADLK
#define EBFONT 59 /* Bad font file format */错误的字体文件格式
#define ENOSTR 60 /* Device not a stream */设备不是流
#define ENODATA 61 /* No data available */无数据
#define ETIME 62 /* Timer expired */计时器到期
#define ENOSR 63 /* Out of streams resources */流资源不足
#define ENONET 64 /* Machine is not on the network */机器不在网络上
#define ENOPKG 65 /* Package not installed */包未安装
#define EREMOTE 66 /* Object is remote */对象是远程
#define ENOLINK 67 /* Link has been severed */链接正在服务中
#define EADV 68 /* Advertise error */广告错误
#define ESRMNT 69 /* Srmount error */？
#define ECOMM 70 /* Communication error on send */发送过程中通讯错误
#define EPROTO 71 /* Protocol error */协议错误
#define EMULTIHOP 72 /* Multihop attempted */多跳尝试
#define EDOTDOT 73 /* RFS specific error */RFS特定错误
#define EBADMSG 74 /* Not a data message */不是数据类型消息
#define EOVERFLOW 75 /* Value too large for defined data type */对指定的数据类型来说值太大
#define ENOTUNIQ 76 /* Name not unique on network */网络上名字不唯一
#define EBADFD 77 /* File descriptor in bad state */文件描述符状态错误
#define EREMCHG 78 /* Remote address changed */远程地址改变
#define ELIBACC 79 /* Can not access a needed shared library */无法访问需要的共享库
#define ELIBBAD 80 /* Accessing a corrupted shared library */访问损坏的共享库
#define ELIBSCN 81 /* .lib section in a.out corrupted */库部分在a.out损坏
#define ELIBMAX 82 /* Attempting to link in too many shared libraries */试图链接太多的共享库
#define ELIBEXEC 83 /* Cannot exec a shared library directly */不能直接运行共享库
#define EILSEQ 84 /* Illegal byte sequence */非法字节序
#define ERESTART 85 /* Interrupted system call should be restarted */应重新启动被中断的系统调用
#define ESTRPIPE 86 /* Streams pipe error */流管错误
#define EUSERS 87 /* Too many users */用户太多
#define ENOTSOCK 88 /* Socket operation on non-socket */在非套接字上进行套接字操作
#define EDESTADDRREQ 89 /* Destination address required */需要目的地址
#define EMSGSIZE 90 /* Message too long */消息太长
#define EPROTOTYPE 91 /* Protocol wrong type for socket */错误协议类型
#define ENOPROTOOPT 92 /* Protocol not available */协议不可用
#define EPROTONOSUPPORT 93 /* Protocol not supported */不支持协议
#define ESOCKTNOSUPPORT 94 /* Socket type not supported */不支持套接字类型
#define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */操作上不支持传输端点
#define EPFNOSUPPORT 96 /* Protocol family not supported */不支持协议族
#define EAFNOSUPPORT 97 /* Address family not supported by protocol */协议不支持地址群
#define EADDRINUSE 98 /* Address already in use */地址已被使用
#define EADDRNOTAVAIL 99 /* Cannot assign requested address */无法分配请求的地址
#define ENETDOWN 100 /* Network is down */网络已关闭
#define ENETUNREACH 101 /* Network is unreachable */网络不可达
#define ENETRESET 102 /* Network dropped connection because of reset */网络由于复位断开连接
#define ECONNABORTED 103 /* Software caused connection abort */软件导致连接终止
#define ECONNRESET 104 /* Connection reset by peer */连接被对方复位
#define ENOBUFS 105 /* No buffer space available */没有可用的缓存空间
#define EISCONN 106 /* Transport endpoint is already connected */传输端点已连接
#define ENOTCONN 107 /* Transport endpoint is not connected */传输端点未连接
#define ESHUTDOWN 108 /* Cannot send after transport endpoint shutdown */传输端点关闭后不能在发送
#define ETOOMANYREFS 109 /* Too many references: cannot splice */太多的引用：无法接合
#define ETIMEDOUT 110 /* Connection timed out */连接超时
#define ECONNREFUSED 111 /* Connection refused */连接被拒绝
#define EHOSTDOWN 112 /* Host is down */主机已关闭
#define EHOSTUNREACH 113 /* No route to host */无法路由到主机
#define EALREADY 114 /* Operation already in progress */操作已在进程中
#define EINPROGRESS 115 /* Operation now in progress */进程中正在进行的操作
#define ESTALE 116 /* Stale NFS file handle */
#define EUCLEAN 117 /* Structure needs cleaning */
#define ENOTNAM 118 /* Not a XENIX named type file */
#define ENAVAIL 119 /* No XENIX semaphores available */
#define EISNAM 120 /* Is a named type file */
#define EREMOTEIO 121 /* Remote I/O error */
#define EDQUOT 122 /* Quota exceeded */
#define ENOMEDIUM 123 /* No medium found */
#define EMEDIUMTYPE 124 /* Wrong medium type */
读，写，定位函数
write
read
lseek
注：offset的值正往右偏移，负往左偏移
lseek(fd,0,SEEK_SET);//从头的位置开始读，偏移0位
lseek(fd,0,SEEK_CUR);//从当前位置开始读，偏移0位
lseek(fd,0,SEEK_END);//从尾的位置开始读，偏移0位
例题：打开一个文件，若文件不存在则创建，并往里写东西
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
void main()
{
int state,len,offset;
char buf[30]={0};
int fd=open("/home/dhh/c.d/tttt.txt",O_RDWR|O_CREAT,0755);
if(fd==-1)
{
printf("errno:%d,errno:%s\n",errno,strerror(errno));
}
else
{
printf("fd:%d,create file successful!\n ",fd);
}
//operate
write(fd,"i heat you!\n",12);//此时指针指向！后的0
printf("offset:%d\n",lseek(fd,0,SEEK_CUR));
lseek(fd,-12,SEEK_CUR);//把指针移到文件开头
len=read(fd,buf,12);
printf("already read:%d\n",len);
printf("read string:%s\n",buf);
//close
state=close(fd);
if(state==0)
{
printf("close file successful!\n");
}
else if(state==-1)
{
printf("errno:%d,errno:%s\n",errno,strerror(errno));
}
}
用cat在控制台查看文件内容可以发现，程序执行前内容为空，执行后内容为所写的值
