文件编程实战

一、4月「掘金·日新计划」第2天

二、打开/创建文件

2.1、open 2参数

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int open(const char *pathname, int flags);

参数：

0. 要打开的文件名

1. 什么权限打开，下面常数是互斥的只能选一个

   0. O_RDWR，可读可写

   1. O_RDONLY，只读

   2. O_WRONLY，只写

   • 可选常数，与前面常数 | 形式追加

     0. O_CREAT，文件不存在创建它，用此选项需要说明参数3mode
     1. O_EXCL，与上面O_CREAT搭配用，如果文件存在则返回－1
     2. O_APPEND，打开文件光标指向文件尾
     3. O_TRUNC，清除文件内容

返回值：

0. 文件描述符，成功返回描述符，失败-1
1. 错误返回-1，并errno被设置 perror()函数打印 可以printf直接打印errno的值，int型，需要加头文件#include <errno.h>

2.2、open 3参数

int open(const char *pathname, int flags, mode_t mode);

参数3：是创建文件时加的权限0600

当前组，同组，其他组

0. 可读 r 4 可写 w 2 可执行 x 1
1. 6=4+2，所以是可读可写权限
2. 0 表示十进制 6 当前用户 0 同组用户 0 其他用户

2.3、creat 创建文件

int creat(const char *pathname, mode_t mode);

参数：

0. 创建的文件名(/文件名，/绝对路径，./当前路径)

1. 权限

   0. S_IRUSR:可读 4
   1. S_IWUSR:可写 2
   2. S_IXUSR:可执行 1
   3. S_IRWXU:可读可写可执行 7

返回值：

0. 文件描述符，成功返回描述符，失败-1

2.4、errno错误码

perror()函数打印 可以printf直接打印errno的值，int型，需要加头文件#include <errno.h>

值 宏 说明 /usr/include/asm-generic/errno-base.h 1 EPERM Operation not permitted 2 ENOENT No such file or directory 3 ESRCH No such process 4 EINTR Interrupted system call 5 EIO I/O error 6 ENXIO No such device or address 7 E2BIG Argument list too long 8 ENOEXEC Exec format error 9 EBADF Bad file number 10 ECHILD No child processes 11 EAGAIN Try again 12 ENOMEM Out of memory 13 EACCES Permission denied 14 EFAULT Bad address 15 ENOTBLK Block device required 16 EBUSY Device or resource busy 17 EEXIST File exists 18 EXDEV Cross-device link 19 ENODEV No such device 20 ENOTDIR Not a directory 21 EISDIR Is a directory 22 EINVAL Invalid argument 23 ENFILE File table overflow 24 EMFILE Too many open files 25 ENOTTY Not a typewriter 26 ETXTBSY Text file busy 27 EFBIG File too large 28 ENOSPC No space left on device 29 ESPIPE Illegal seek 30 EROFS Read-only file system 31 EMLINK Too many links 32 EPIPE Broken pipe 33 EDOM Math argument out of domain of func 34 ERANGE Math result not representable /usr/include/asm-generic/errno.h 35 EDEADLK或EDEADLOCK Resource deadlock would occur 36 ENAMETOOLONG File name too long 37 ENOLCK No record locks available 38 ENOSYS Invalid system call number 39 ENOTEMPTY Directory not empty 40 ELOOP Too many symbolic links encountered 41(EAGAIN) EWOULDBLOCK Operation would block 42 ENOMSG No message of desired type 43 EIDRM Identifier removed 44 ECHRNG Channel number out of range 45 EL2NSYNC Level 2 not synchronized 46 EL3HLT Level 3 halted 47 EL3RST Level 3 reset 48 ELNRNG Link number out of range 49 EUNATCH Protocol driver not attached 50 ENOCSI No CSI structure available 51 EL2HLT Level 2 halted 52 EBADE Invalid exchange 53 EBADR Invalid request descriptor 54 EXFULL Exchange full 55 ENOANO No anode 56 EBADRQC Invalid request code 57 EBADSLT Invalid slot 59 EBFONT Bad font file format 60 ENOSTR Device not a stream 61 ENODATA No data available 62 ETIME Timer expired 63 ENOSR Out of streams resources 64 ENONET Machine is not on the network 65 ENOPKG Package not installed 66 EREMOTE Object is remote 67 ENOLINK Link has been severed 68 EADV Advertise error 69 ESRMNT Srmount error 70 ECOMM Communication error on send 71 EPROTO Protocol error 72 EMULTIHOP Multihop attempted 73 EDOTDOT RFS specific error 74 EBADMSG Not a data message 75 EOVERFLOW Value too large for defined data type 76 ENOTUNIQ Name not unique on network 77 EBADFD File descriptor in bad state 78 EREMCHG Remote address changed 79 ELIBACC Can not access a needed shared library 80 ELIBBAD Accessing a corrupted shared library 81 ELIBSCN .lib section in a.out corrupted 82 ELIBMAX Attempting to link in too many shared libraries 83 ELIBEXEC Cannot exec a shared library directly 84 EILSEQ Illegal byte sequence 85 ERESTART Interrupted system call should be restarted 86 ESTRPIPE Streams pipe error 87 EUSERS Too many users 88 ENOTSOCK Socket operation on non-socket 89 EDESTADDRREQ Destination address required 90 EMSGSIZE Message too long 91 EPROTOTYPE Protocol wrong type for socket 92 ENOPROTOOPT Protocol not available 93 EPROTONOSUPPORT Protocol not supported 94 ESOCKTNOSUPPORT Socket type not supported 95 EOPNOTSUPP Operation not supported on transport endpoint 96 EPFNOSUPPORT Protocol family not supported 97 EAFNOSUPPORT Address family not supported by protocol 98 EADDRINUSE Address already in use 99 EADDRNOTAVAIL Cannot assign requested address 100 ENETDOWN Network is down 101 ENETUNREACH Network is unreachable 102 ENETRESET Network dropped connection because of reset 103 ECONNABORTED Software caused connection abort 104 ECONNRESET Connection reset by peer 105 ENOBUFS No buffer space available 106 EISCONN Transport endpoint is already connected 107 ENOTCONN Transport endpoint is not connected 108 ESHUTDOWN Cannot send after transport endpoint shutdown 109 ETOOMANYREFS Too many references: cannot splice 110 ETIMEDOUT Connection timed out 111 ECONNREFUSED Connection refused 112 EHOSTDOWN Host is down 113 EHOSTUNREACH No route to host 114 EALREADY Operation already in progress 115 EINPROGRESS Operation now in progress 116 ESTALE Stale file handle 117 EUCLEAN Structure needs cleaning 118 ENOTNAM Not a XENIX named type file 119 ENAVAIL No XENIX semaphores available 120 EISNAM Is a named type file 121 EREMOTEIO Remote I/O error 122 EDQUOT Quota exceeded 123 ENOMEDIUM No medium found 124 EMEDIUMTYPE Wrong medium type 125 ECANCELED Operation Canceled 126 ENOKEY Required key not available 127 EKEYEXPIRED Key has expired 128 EKEYREVOKED Key has been revoked 129 EKEYREJECTED Key was rejected by service 130 EOWNERDEAD Owner died 131 ENOTRECOVERABLE State not recoverable 132 ERFKILL Operation not possible due to RF-kill 133 EHWPOISON Memory page has hardware error ———————————————— 版权声明：本文为CSDN博主「邻居家的小南瓜」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。 原文链接：blog.csdn.net/qq_37932504…

三、写文件

3.1、write

#include <unistd.h>
ssize_t write(int fd, const void *buf, size_t count);

参数：

0. 文件描述符
1. 缓冲区，写入内容
2. 写入大小，字节strlen

返回值：

0. 写入的个数
1. 失败-1

四、读文件

4.1、read

#include <unistd.h>
ssize_t read(int fd, void *buf, size_t count);

参数：

0. 文件描述符
1. 缓冲区，读到哪里
2. 读取大小，字节strlen

返回值：

0. 读取个数
1. 失败-1

五、光标

5.1、lseek

#include <sys/types.h>
#include <unistd.h>
off_t lseek(int fd, off_t offset, int whence)

参数：

0. 文件描述符

1. 偏移值，0不偏移，正往后，负往前 针对whence偏移

2. 光标移动到位置

   0. SEEK_SET，头
   1. SEEK_END，尾
   2. SEEK_CUR，当前位置

返回值：

0. 偏移值，针对文件头，计算文件大小
1. 错误返回-1
2. errno被设置 perror()函数打印

六、关闭文件

6.1、close

#include <unistd.h>
int close(int fd);

参数：

0. 文件描述符