Move the cursor in a C program

Question

I'd like to move the cursor forward and backwards in a C program. I'm reading the whole line in a loop, but i would like that if a cursor key gets pressed the cursor on the screen changes position, without blocking the loop. I tried getwch() but it blocks the caller until enter it's pressed. What i'm looking for is a behavior similar to bash prompt. I'm reading with a code similar to this:

while (TRUE) {    printf("%s", PROMPT);    fgets(input, 1024, stdin);    do_something(input); } 

I'm trying that the function above works like readline(PROMPT) on the readline.h library

Answer 1

Using termios and console-codes (VT100 compatible - not portable):

#include <stdio.h> #include <string.h> #include <termios.h> #include <unistd.h>  #define cursorforward(x) printf("\033[%dC", (x)) #define cursorbackward(x) printf("\033[%dD", (x))  #define KEY_ESCAPE  0x001b #define KEY_ENTER   0x000a #define KEY_UP      0x0105 #define KEY_DOWN    0x0106 #define KEY_LEFT    0x0107 #define KEY_RIGHT   0x0108  static struct termios term, oterm;  static int getch(void); static int kbhit(void); static int kbesc(void); static int kbget(void);  static int getch(void) {     int c = 0;      tcgetattr(0, &oterm);     memcpy(&term, &oterm, sizeof(term));     term.c_lflag &= ~(ICANON | ECHO);     term.c_cc[VMIN] = 1;     term.c_cc[VTIME] = 0;     tcsetattr(0, TCSANOW, &term);     c = getchar();     tcsetattr(0, TCSANOW, &oterm);     return c; }  static int kbhit(void) {     int c = 0;      tcgetattr(0, &oterm);     memcpy(&term, &oterm, sizeof(term));     term.c_lflag &= ~(ICANON | ECHO);     term.c_cc[VMIN] = 0;     term.c_cc[VTIME] = 1;     tcsetattr(0, TCSANOW, &term);     c = getchar();     tcsetattr(0, TCSANOW, &oterm);     if (c != -1) ungetc(c, stdin);     return ((c != -1) ? 1 : 0); }  static int kbesc(void) {     int c;      if (!kbhit()) return KEY_ESCAPE;     c = getch();     if (c == '[') {         switch (getch()) {             case 'A':                 c = KEY_UP;                 break;             case 'B':                 c = KEY_DOWN;                 break;             case 'C':                 c = KEY_LEFT;                 break;             case 'D':                 c = KEY_RIGHT;                 break;             default:                 c = 0;                 break;         }     } else {         c = 0;     }     if (c == 0) while (kbhit()) getch();     return c; }  static int kbget(void) {     int c;      c = getch();     return (c == KEY_ESCAPE) ? kbesc() : c; }  int main(void) {     int c;      while (1) {         c = kbget();         if (c == KEY_ENTER || c == KEY_ESCAPE || c == KEY_UP || c == KEY_DOWN) {             break;         } else         if (c == KEY_RIGHT) {             cursorbackward(1);         } else         if (c == KEY_LEFT) {             cursorforward(1);         } else {             putchar(c);         }     }     printf("\n");     return 0; }