一、对终端进行读写
当一个程序在命令提示符中被调用时,
shell负责将标准输入和标准输出流连接到你的程序,
实现程序与用户间的交互。
1. 标准模式和非标准模式
在默认情况下,
只有用户按下回车键后,程序才能读到终端的输入。
在大多数情况下,这样做是有益的,
因为它允许用户使用退格键和删除键来纠正输入中的错误,
用户只在对自己在屏幕上看到的内容满意时,
才会按下回车键把键入的数据传递给程序。
这种方式称为规范模式或标准模式。
在这种方式下,
Linux会暂存用户输入的内容,
直到用户按下回车键,
然后将用户选择的字符及紧随其后的回车符一起传递给程序。
2. 与终端进行对话
Linux提供了一个特殊设备/dev/tty,
该设备始终是指向当前终端或当前登录会话。
二、termios结构
termios是在POSIX规范中定义的标准接口,
通过设置termios类型的数据结构中的值和使用一小组函数调用,
就可以对终端接口进行控制。
termios数据结构和相关函数调用都定义在头文件termios.h中。
可以被调整来影响终端的值按照不同的模式被分成如下几组:
输入模式
输出模式
控制模式
本地模式
特殊控制字符
最小的termios结构的典型定义如下:
- #include <termios.h>
- struct termios {
- tcflag_t c_iflag;
- tcflag_t c_oflag;
- tcflag_t c_cflag;
- tcflag_t c_lflag;
- cc_t c_cc[NCCS];
- };
结构成员名称与上面列出的5种参数类型相对应。
可以调用函数tcgetattr来初始化与一个终端对应的termios结构,
该函数的原型如下:
- #include <termios.h>
- int tcgetattr(int fd, struct termios *termios_p);
这个函数调用把当前终端接口变量的值写入termios_p参数指向的结构。
如果这些值其后被修改了,
可以通过调用函数tcsetattr来重新配置终端接口,
该函数的原型如下:
- #include <termios.h>
- int tcsetattr(int fd, int actions, const struct termios *termios_p);
参数actions控制修改方式,
共有3种修改方式:
TCSANOW: 立刻对值进行修改
TCSADRAIN: 等当前的输出完成后再对值进行修改
FCSAFLUSH: 等当前的输出完成后再对值进行修改,
但丢弃还未从read调用返回的当前可用的任何输入。
具体的模式的宏定义可以参见man帮助手册或相关文档。
1. 输入模式
termios结构中的c_iflag成员的标志对它们进行控制。
可用于c_iflag成员的宏如下所示:
❑ BRKINT: Generate an interrupt when a break condition (loss of connection)
is detected on the line
❑ IGNBRK: Ignore break conditions on the line
❑ ICRNL: Convert a received carriage return to a newline
❑ IGNCR: Ignore received carriage returns
❑ INLCR: Convert received newlines to carriage returns
❑ IGNPAR: Ignore characters with parity errors
❑ INPCK: Perform parity checking on received characters
❑ PARMRK: Mark parity errors
❑ ISTRIP: Strip (set to seven bits) all incoming characters
❑ IXOFF: Enable software flow control on input
❑ IXON: Enable software flow control on output
2. 输出模式
c_oflag成员的宏如下所示:
❑ OPOST: Turn on output processing
❑ ONLCR: Convert any output newline to a carriage return/line feed pair
❑ OCRNL: Convert any output carriage return to a newline
❑ ONOCR: No carriage return output in column 0
❑ ONLRET: A newline also does a carriage return
❑ OFILL: Send fill characters to provide delays
❑ OFDEL: Use DEL as a fill character, rather than NULL
❑ NLDLY: Newline delay selection
❑ CRDLY: Carriage return delay selection
❑ TABDLY: Tab delay selection
❑ BSDLY: Backspace delay selection
❑ VTDLY: Vertical tab delay selection
❑ FFDLY: Form feed delay selection
3. 控制模式
c_cflag成员的宏如下所示:
❑ CLOCAL: Ignore any modem status lines.
❑ CREAD: Enable the receipt of characters.
❑ CS5: Use five bits in sent or received characters.
❑ CS6: Use six bits in sent or received characters.
❑ CS7: Use seven bits in sent or received characters.
❑ CS8: Use eight bits in sent or received characters.
❑ CSTOPB: Use two stop bits per character, rather than one.
❑ HUPCL: Hang up modem on close.
❑ PARENB: Enable parity generation and detection.
❑ PARODD: Use odd parity rather than even parity.
4. 本地模式
c_lflag成员的宏如下所示:
❑ ECHO: Enable local echoing of input characters
❑ ECHOE: Perform a Backspace, Space, Backspace combination on receiving ERASE
❑ ECHOK: Perform erase line on the KILL character
❑ ECHONL: Echo newline characters
❑ ICANON: Enable canonical input processing (see the text following this list)
❑ IEXTEN: Enable implementation-specific functions
❑ ISIG: Enable signals
❑ NOFLSH: Disable flush on queue
❑ TOSTOP: Send background processes a signal on write attempts
5. 特殊控制字符
c_cc数组:
标准模式中可使用的数组下标:
❑ VEOF: EOF character
❑ VEOL: EOL character
❑ VERASE: ERASE character
❑ VINTR: INTR character
❑ VKILL: KILL character
❑ VQUIT: QUIT character
❑ VSUSP: SUSP character
❑ VSTART: START character
❑ VSTOP: STOP character
非标准模式中可使用的数组下标:
❑ VINTR: INTR character
❑ VMIN: MIN value
❑ VQUIT: QUIT character
❑ VSUSP: SUSP character
❑ VTIME: TIME value
❑ VSTART: START character
❑ VSTOP: STOP character
6. 终端速度
函数原型如下:
- #include <termios.h>
- speed_t cfgetispeed(const struct termios *);
- speed_t cfgetospeed(const struct termios *);
- int cfsetispeed(struct termios *, speed_t speed);
- int cfsetospeed(struct termios *, speed_t speed);
7. 其他函数
- #include <termios.h>
- int tcdrain(int fd);
- int tcflow(int fd, int flowtype);
- int tcflush(int fd, int in_out_selector);
三、ffmpeg对键盘响应程序的分析
main.c
- /*
- * \File
- * main.c
- * \Descript
- * Taken from ffmpeg,
- * implement for signal response function
- * \Author
- * Neo Yan
- */
- #include <stdio.h>
- #include <stdlib.h>
- #include <signal.h>
- #include <limits.h>
- #include <unistd.h>
- #include <fcntl.h>
- #include <sys/ioctl.h>
- #include <sys/time.h>
- #include <termios.h>
- static struct termios oldtty;
- static int q_pressed = 0;
- static int verbose = 1;
- static int using_stdin = 0;
- static int run_as_daemon = 0;
- static volatile int received_sigterm = 0;
- static void term_init(void);
- static void term_exit(void);
- static void sigterm_handler(int sig);
- static int read_key(void);
- /*
- * \Func
- * main
- * \Descript
- *
- */
- int main(int argc, char **argv)
- {
- int index = 0;
- int key;
- if (!using_stdin)
- {
- if (verbose >= 0)
- printf("Perss [q] to stop, [?] for help\n");
- }
- term_init();
- for ( ; received_sigterm == 0; )
- {
- /* if 'q' pressed, exits */
- if (!using_stdin)
- {
- if (q_pressed)
- break;
- /* read_key() returns 0 on EOF */
- key = read_key();
- if (key == 'q')
- {
- printf("quit\n");
- break;
- }
- if (key == '+')
- {
- verbose++;
- printf("verbose = %d\n", verbose);
- }
- if (key == '-')
- {
- verbose--;
- printf("verbose = %d\n", verbose);
- }
- if (key == '?')
- {
- printf("key function\n"
- "? show this help\n"
- "+ increase verbosity\n"
- "- decrease verbosity\n"
- "q quit\n"
- );
- }
- }
- printf("index = %d\n", index++);
- sleep(1);
- }
- return 0;
- }
- static void term_init(void)
- {
- if (!run_as_daemon)
- {
- struct termios tty;
- tcgetattr(0, &tty);
- oldtty = tty;
- atexit(term_exit);
- tty.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP
- |INLCR|IGNCR|ICRNL|IXON);
- tty.c_oflag |= OPOST;
- tty.c_lflag &= ~(ECHO|ECHONL|ICANON|IEXTEN);
- tty.c_cflag &= ~(CSIZE|PARENB);
- tty.c_cflag |= CS8;
- tty.c_cc[VMIN] = 1;
- tty.c_cc[VTIME] = 0;
- tcsetattr (0, TCSANOW, &tty);
- /* Quit (POSIX). */
- signal(SIGQUIT, sigterm_handler);
- }
- signal(SIGINT , sigterm_handler);
- signal(SIGTERM, sigterm_handler);
- }
- static void term_exit(void)
- {
- printf("%s\n", "TERMINATION");
- if (!run_as_daemon)
- tcsetattr(0, TCSANOW, &oldtty);
- }
- static void sigterm_handler(int sig)
- {
- received_sigterm = sig;
- q_pressed++;
- term_exit();
- }
- /*
- * \Func
- * read_key
- * \Descript
- * read a key without blocking
- */
- static int read_key(void)
- {
- int n = 1;
- unsigned char ch;
- struct timeval tv;
- fd_set rfds;
- if (run_as_daemon)
- return -1;
- FD_ZERO(&rfds);
- FD_SET(0, &rfds);
- tv.tv_sec = 0;
- tv.tv_usec = 0;
- n = select(1, &rfds, NULL, NULL, &tv);
- if (n > 0)
- {
- n = read(0, &ch, 1);
- if (n == 1)
- return ch;
- return n;
- }
- return -1;
- }
makefile
- OBJECTS = main.o
- CC = gcc
- CFLAG = -g
- ffmpeg_signal : $(OBJECTS)
- $(CC) $(CFLAG) -o ffmpeg_signal $(OBJECTS)
- main.o:
- .PHONY:clean
- clean:
- rm ffmpeg_signal $(OBJECTS)