• C

C Programming: Code Review

I am getting extra characters in the ouput of my program. The "t" is an example of the extra character I'm getting. Not sure what can be causing this. I though maybe buffer overflow, so I removed all functions like strcpy and strcat from the readInput method, but the problem is still happening.

Here is a sampleoutput:

$
$ ./yak /dev/pts/3
pz951772@/dev/pts/3: test
pz951772@/dev/pts/3: test
pz951772@/dev/pts/3: hi
pz951772@/dev/pts/3: hi
t
pz951772@/dev/pts/3:


#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)
        break;
   }
   close(fd);
}

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';
   //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");
   //fgets(buffer, count, stdin);

   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;
}

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pzozulkaAsked:
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ozoCommented:
// read
   if(( bytes_read = read(STDIN_FILENO, buffer, count-1)) == -1){
        perror("read() error");
   }else{
        bytes_read[buffer]='\0';
   }
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pzozulkaAuthor Commented:
I was wondering if you could also help me figure out why ^d doesn't quit the program.

It use to work (line 28) when I was using buffered IO, but now I'm using raw IO and it no longer works. Any suggestions?
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