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C Programming: Code question

When I run this code, the print command runs fine on line 15, but no other print command our any kind of output happens after that line (including line 18).

I have a feeling it has something to do with the READ code on line 74.

This is for a project that requires me to use open(2), write(2), read(2), etc.

#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 void writeLine(char *b, int filedes);
static void readInput(const char *u, char *b);

int main( int argc, char *argv[] ) {
   printf("test\n");

   char *t = "This is a test";
   printf("%s",t);
   struct passwd *mypasswd;
   int fd;
   char *usr = malloc(sizeof(char) * 1024);
   char *buf = malloc(sizeof(char) * 1024);
   char *mytty;

   //printf("test2\n");

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

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

      strcpy(usr, user);
      strcat(usr, "@");
      strcat(usr, mytty);
      strcat(usr, ": ");
   }
   printf("a");
   //open file
   fd = open(argv[1], O_RDWR);
   printf("0");
   while(!feof(stdin)) {
     printf("1");
     readInput(usr, buf);
     printf("2");
     writeLine(buf, fd);
   }

   close(fd);
}

static void writeLine(char *b, int filedes) {
   size_t nbytes;
   ssize_t bytes_written;

   nbytes = strlen(b);
   if(( bytes_written = write(filedes, b, nbytes)) == -1)
        perror("write() error");
}

static void readInput(const char *u, char *b) {
   printf("1.1");

   ssize_t bytes_written;
   size_t count = 200;
   int max_input = 200;
   char buffer[max_input];

   strcpy(b, "");
   printf("%s", u);

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

   // append user input to *b string
   strcat(b, u);
   strcat(b, buffer);
}

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Kent Olsen

Howdy....

There are variations in how printf() is implemented. The standards have changed over the years.

Try calling fflush (stdout). That may solve your problem.

Kent

pzozulka

ASKER

Thanks, but that didn't help. When I comment out the READ line of code, everything works as expected.

ASKER CERTIFIED SOLUTION

Kent Olsen

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pzozulka

ASKER

I meant to say that I'm either using READ or FGETS. When I use FGETS everything works as expected, but when I use READ it makes all of my PRINTF functions stop working -- even before I get to the point where I call READ.

Example:
// Application works fine when:

static void readInput(const char *u, char *b) {

   ssize_t bytes_read;
   size_t count = 200;
   int max_input = 200;
   char buffer[max_input];

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

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

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Application behaving incorrectly when using:

static void readInput(const char *u, char *b) {

   ssize_t bytes_read;
   size_t count = 200;
   int max_input = 200;
   char buffer[max_input];

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

   // read
   if(( bytes_read = read(STDIN_FILENO, buffer, count)) == -1)
        perror("read() error");
   // append user input to *b string
   //strcat(b, u);
   strcat(b, buffer);
}

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