Unix/Linux编程实践教程笔记【chap01】

1. /dev/tty
   /dev/tty是键盘和显示器的设备描述文件，向这个文件写相当于显示在屏幕上，向这个文件读相当于从键盘读取输入，即使程序用’<’和‘>’重定位了标准输入和输出，依然可以通过这个文件和终端交换数据。

more01.cpp:

/*more01.cpp - version 0.1 of more
  read and print 24 lines then pause for a few special conmands
*/

#include <stdio.h>
#include <stdlib.h>
#define PAGELEN 24
#define LINELEN 512

void do_more(FILE *);
int see_more();

int main(int argc, char* argv[])
{
    FILE *fp;
    if(argc==1)
        do_more(stdin);
    else
    {
        while(argc--)
        {
            if((fp=fopen(*++argv,"r"))!=NULL)
            {
                do_more(fp);
                fclose(fp);
            }
            else
            {
                exit(1);
            }
        }
    }
    exit(0);
}

void do_more(FILE *fp)
/*
 *read PAGELEN lines, then call see_more() for further instructions
 */
{
    char line[LINELEN];
    int num_of_lines = 0;
    int see_more(),reply;

    while(fgets(line,LINELEN,fp))  //more input
    {
        if(num_of_lines==PAGELEN)
        {
            reply = see_more();
            if(reply==0)
                break;
            num_of_lines -= reply;
        }

        if(fputs(line,stdout)==EOF)
            exit(1);
        num_of_lines++;
    }
}

int see_more()
/*
 *print message,wait for response,return # of lines to advance
 *q means no, space means yes, CR means one lines
 */
{
    int c;
    printf("\033[7m more?\033[m");

    while((c=getchar())!=EOF)
    {
        if(c=='q')
            return 0;

        if(c==' ')
            return PAGELEN;

        if(c=='\n')
            return 1;
    }

    return 0;
}

more02.cpp

/* more02.cpp - version 0.2 of more
 * read and print 24 lines then pause for a few specoal commands
 * feature of version 0.2 : reads from /dev/tty for commands
 */

#include <stdio.h>
#include <stdlib.h>
#define PAGELEN 24
#define LINELEN 512

void do_more(FILE *fp);
int see_more(FILE *fp);

int main(int argc, char* argv[])
{
    FILE *fp;

    if(argc==1)
        do_more(stdin);
    else
    {
        while(--argc)
        {
            if((fp=fopen(*++argv,"r"))!=NULL)
            {
                do_more(fp);
                fclose(fp);
            }
            else
                exit(1);
        }
    }

    exit(0);
}

void do_more(FILE *fp)
/*
 *read PAGELEN lines,then call see_more() for further instructions
 */
{
    char line[LINELEN];
    int num_of_lines = 0;
    int see_more(FILE*),reply;
    FILE *fp_tty;

    fp_tty = fopen("/dev/tty","r");
    if(fp_tty==NULL)
        exit(1);

    while(fgets(line,LINELEN,fp))
    {
        if(num_of_lines==PAGELEN)
        {
            reply = see_more(fp_tty);

            if(reply==0)
                break;
            num_of_lines -= reply;
        }

        if(fputs(line,stdout)==EOF)
            exit(1);

        num_of_lines++;
    }
}

int see_more(FILE* cmd)
/*
 *print message,wait for response,return # of lines to advance
 *q means no, space means yes,CR means one line
 */
{
    int c;
    printf("\033[7m more? \033[m");
    while((c=getc(cmd))!=EOF)
    {
        if(c=='q')
            return 0;

        if(c==' ')
            return PAGELEN;

        if(c=='\n')
            return 1;
    }

    return 0;
}