Linux环境高级编程
open 函数
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
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 <unistd.h>
ssize_t write(int fd, const void *buf, size_t count);
read
#include <unistd.h>
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 <string.h>
char *strerror(int errnum);
#include <stdio.h>
void perror(const char *s);
lseek
lseek - reposition read/write file offset
#include <sys/types.h>
#include <unistd.h>
off_t lseek(int fd, off_t offset, int whence);
