Linux环境高级编程

Linux环境高级编程

open 函数

   #include 
   #include 
   #include 

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

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

write

   #include 

   ssize_t write(int fd, const void *buf, size_t count);

read
#include

   ssize_t read(int fd, void *buf, size_t count);

ssize_t 有符号类型，（typedef定义）

查看最大打开文件个数的限制（ulimit -a）

ulimit -a

ulimit -n 4096 (设置)

core file size  (blocks, -c) 0
data seg size   (kbytes, -d) unlimited
scheduling priority (-e) 0
file size   (blocks, -f) unlimited
pending signals (-i) 7976
max locked memory   (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files  (-n) 65536
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) 7976
virtual memory  (kbytes, -v) unlimited
file locks  (-x) unlimited

查看当前系统允许最大文件个数cat /proc/sys/fs/file-max

文件描述符

STDIN_FILENO 0
STDOUT_FILENO 1

error 头文件 errno的值

/usr/include/asm-generic/errno-base.h
/usr/include/asm-generic/errno.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 */

报错的时候把错误码写入errno，strerror(errno)可以得到错误的解释，perror()也可以得到错误的解释

   #include 

   char *strerror(int errnum);

   #include 

   void perror(const char *s);

lseek

   lseek - reposition read/write file offset

   #include 
   #include 
   off_t lseek(int fd, off_t offset, int whence);