Linux程序设计第四版 笔记

1：5.2节中与终端进行对话

      如果不希望程序中与用户交互的部分被重定向，单允许其他的输入和输出呗重定向，你就需要将与用户交互的部分与stdout和stderr分开，因此，可以直接对/dev/tty进行读写，该设备始终指向当前终端或当前的登录会话。代码如下：

#include <stdio.h>#include <unistd.h>char *menu[] = {    "a - add new record",    "d - delete record",    "q - quit",    NULL,};int getchoice(char *greet, char *choices[], FILE *in, FILE *out);int main(){    int choice = 0;    FILE *input;    FILE *output;    if (!isatty(fileno(stdout))) {        fprintf(stderr,"You are not a terminal, OK.\n");    }    input = fopen("/dev/tty", "r");    output = fopen("/dev/tty", "w");    if(!input || !output) {         fprintf(stderr,"Unable to open /dev/tty\n");        exit(1);    }    do {        choice = getchoice("Please select an action", menu, input, output);        printf("You have chosen: %c\n", choice);    } while (choice != 'q');    exit(0);}int getchoice(char *greet, char *choices[], FILE *in, FILE *out){    int chosen = 0;    int selected;    char **option;    do {        fprintf(out,"Choice: %s\n",greet);        option = choices;        while(*option) {            fprintf(out,"%s\n",*option);            option++;        }        do {            selected = fgetc(in);        } while (selected == '\n');        option = choices;        while(*option) {            if(selected == *option[0]) {                chosen = 1;                break;            }            option++;        }        if(!chosen) {            fprintf(out,"Incorrect choice, select again\n");        }    } while(!chosen);    return selected;}

执行效果：

$ ./a.out >file
You are not a terminal, OK.
Choice: Please select an action
a - add new record
d - delete record
q - quit
d
Choice: Please select an action
a - add new record
d - delete record
q - quit
q
$ cat file
You have chosen: d
You have chosen: q
$ 

源码解析：

其实就是把不需要重定向的信息，即仍然要显示在屏幕上的信息显示在设备/dev/tty中，而本来通过stdin/stdout/stderr的信息就重定向到file文件中了，不显示到屏幕上。