How do you overlap text in C terminal -

one of training exercises in c programming book goes following: (translated swedish)

if use writing/typing terminal kan sometimes, normal typewriter, underline word stepping on line , writing _ under word. write program writes string in variable s underlined.

my attempt looks this:

#include <stdio.h>  int main(void) {   char *s;   printf("input: ");   scanf("%ms", &s);   (int i=0; s[i] != '\0'; i++) {     printf("%c\b_", s[i]);   }   printf("\n");   return 0; } 

this not work expect terminal output be:

$> gcc -wall -std=c99 file.c   $> ./file.c   input: test   test //underlined $> 

but instead get:

$> gcc -wall -std=c99 file.c   $> ./file.c   input: test   ____   $>  

does know how or book wrong?

i haven't found way allow literal rendering of 1 character on another, sadly (i didn't think possible modern terminals, i'm happy proven wrong wumpus q. wumbley has made point piping through less allows this. i've not had time @ how/why works within less though).

i'd propose workaround - there way enable underscoring little more directly using ansi code \033[4m.

modifying code:

#include <stdio.h>  int main() {   char *s;    printf("input: ");   scanf("%ms", &s);   printf("\033[4m"); // enable underlining   printf("%s", s); // print string   printf("\033[0m"); // reset text attributes (disable underlining)   printf("\n");   return 0; } 

you can find other ansi graphic settings in sgr table in csi codes section on wikipedia, here.

the \033 specifies it's terminal escape code, combination of \e [ specifies it's terminal control signal, <number>m specifies we're doing "sgr", "select graphic rendition" command, , number 4 parameter corresponds effect "underline: single". 0 corresponds reset.

i welcome corrections though, don't know ansi code format.

---

i've skimmed through less source, , suspect it's converting sequences _\ba utf underlined characters - haven't quite got bottom of yet.