Thu 8 Feb 15:43:18 GMT 2018
Part III
interaction and communication between Programs
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chapter 10 System-Level I/O
10.1 Unix I/O
<unistd.h> : STDIN_FILENO STDOUT_FILENO STDERR_FILENO
10.2 files
对内核而言，文本文件和二进制文件没有区别
10.3 open and close files
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int open(char *filename, int flags, mode_t mode);
flags:
+ O_RDONLY
+ O_WRONLY
+ O_RDWR
for write:
+ O_CREAT
+ O_TRUNC
+ O_APPEND
fd = open("foo.txt",O_WRONLY|O_APPEND,O);
umask(O_WRONLY);
#include <unistd.h>
int close(int fd);
10.4 read and write files
#include <unistd.h>
ssize_t read(int fd, void *buf, size_t n);
ssize_t write(int fd, const void *buf,size_t n);
lseek function set position.
In the x86-64, size_t means unsigned long and ssize_t
means long type.
10.5 用RIO包健壮地读写（Robust I/O)
RIO提供两类不同函数：
+ 无缓冲的输入输出函数
对二进制读写网络有用
+ 带缓冲的输入输出函数
对文件中读写有用
10.6 读取文件元数据
应用程序能通过调用stat和fstat函数，检索到关于文件的信
息（有时也称为文件的元数据）。
10.7 读取目录内容
#include <sys/types.h>
#include <dirent.h>
+ DIR *opendir( const char *name);
+ struct dirent *readdir(DIR *dirp);
+ struct dirent {
ino_t d_ino; // inode number
char d_name[256]; // filename
};
+ int closedir(DIR *dirp);
10.8 共享文件
内核用三个相关的数据结构来表示打开的文件：
1. 描述符表(descriptor table).
Each process has its own descriptor tabel.
2. 文件表(file table).
Each file table entry consists of the current
file position, a reference count of the number
of descriptor entries that currently point to it.
The kernel will not delete the file table entry
until its reference count is Zero.
3. v-node表。
Like the file table, the v-node table is shared
by all processes. Each each contains most of the
information in the ‘stat‘ structure, including
the st_mode and st_size members.
10.9 I/O Redirection
#include <unistd.h>
int dup2(int oldfd, int newfd);
10.10 Standard I/O
The libary(libc) provides functions for opening and
closing files( fopen and fclose ), reading and writing
bytes( fread and fwrite ), reading and writing strings
( fgets and fputs ), and sophisticated formatted I/O
( scanf and printf ).
To the programmer, a stream is a pointer to a
structure of type FILE.
10.11 综合：我该使用哪些I/O函数