• C

C Programming: Terminate execution when user input is ^d

The boolean check "!feof(stdin)" inside the while loop on line 28 was working fine when I was using buffered IO. But when I switched to using raw IO it stopped working. The project requires the use of read(2), write(2), open(2), etc.

This started happening when I switched from fgets() to read() on line 73.

My goal is to end the program when the user input is ^d (ctrl + d).

#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <dirent.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <pwd.h>

static int writeLine(const char *b, const char *u, int filedes);
static char* readInput(const char *u, char buffer[]);
static char* getUser();

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

   int fd;
   int max_input = 200;
   char buffer[max_input];
   //char *buf = malloc(sizeof(char) * 1024);

   // get username
   char *myUser = getUser();

   //open file
   fd = open(argv[1], O_RDWR);

   while(!feof(stdin)) {
     char *buf = readInput(myUser, buffer);
     if(writeLine(buf, myUser, fd) < 0)

static char* getUser() {
   struct passwd *mypasswd;
   char *mytty;

   if( (mypasswd = getpwuid(geteuid())) != NULL ) {
      char *user = mypasswd->pw_name;

      if(( mytty = ttyname(STDIN_FILENO)) == NULL)
         perror("ttyname() error");

      int userLen = strlen(user);
      int ttyLen = strlen(mytty);
      char *usr = malloc(sizeof(char) * (userLen + ttyLen + 5));

      strcpy(usr, user);
      strcat(usr, "@");
      strcat(usr, mytty);
      strcat(usr, ": ");

      return usr;

static char* readInput(const char *u, char buffer[]) {

   ssize_t bytes_read;
   size_t count = 200;

   //buffer[0] = '\0';
   //strcpy(b, "");
   //printf("%s", u);

   // display UserName
   if(write(STDOUT_FILENO, u, strlen(u)) < 0)
      perror("write() error");

   // read
   if(( bytes_read = read(STDIN_FILENO, buffer, count)) == -1) {
        perror("read() error");
   else {

   //fgets(buffer, count, stdin);
   // append user input to *b string
   //strcat(b, u);
   //strcat(b, buffer);

   return buffer;

static int writeLine(const char *b, const char *u, int filedes) {
   size_t ulen, blen;

   blen = strlen(b);
   ulen = strlen(u);

   if(write(filedes, u, ulen) < 0 || write(filedes, b, blen) < 0 ) {
        perror("write() error");
        return -1;
   return 0;

Open in new window

Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

if( (bytes_read = read(STDIN_FILENO, buffer, count)) == -1 ){
        perror("read() error");
   }else if(  bytes_read == 0 ){

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
murugesandinsShell_script Automation /bin/bash /bin/bash.exe /bin/ksh /bin/mksh.exe AIX C C++ CYGWIN_NT HP-UX Linux MINGW32 MINGW64 SunOS Windows_NTCommented:
The following change is required for maintaining the source code.
As per the work I used to do in C/C++, I (and all programmers) used to prefer
(  0 == bytes_read )

Open in new window

instead of
(  bytes_read == 0 )

Open in new window

It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.