Linux环境高级编程

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);