get interactive input using glib functions in C

Question

I am writing a c library but before I want to test the functions. So, I do the following:

int main(void)
{
GString *msg = NULL;
msg = g_string_sized_new(256);
printf ("Insert a string (255 characters at most): ");
do_fgets((char *) msg->str, (size_t) msg->len, stdin);
printf("msg->allocated_len = %u \n", (size_t) msg->allocated_len);
printf("msg->len = %u \n", (size_t) msg->len);

return 0;
}

the compile is ok, but the program prints the following: msg->allocated_len = 512 msg->len = 0

Why this? Is there any other way to get interactive input from the user using glib functions?

I'll be grateful if somebody could help me!

Answer 1

I'm assuming the do_fgets is your own function wrapping fgets , anyway...

Your code is failing since it is trying to read 0 bytes (the initial value of msg->len ). Additionally, msg->len is never updated (it is passed to do_fgets by value).

Answer 2

Resurection. I think I've found the solution to my question. What I did is to read the input to a buffer and then assign the buffer to the struct member src an everything is ok: That's the code roughly:

int main(void)
{
  GString *msg = NULL;
  gchar *p;
  gchar buf[256];
  msg = g_string_sized_new(256);
  printf ("Enter a message (255 characters at most): ");
  p = fgets(buf, sizeof(buf), stdin);
  g_string_assign(msg, buf);
  printf("msg->str = [%s] \n", (char *) msg->str);
  printf("msg->len = %u \n", (size_t) msg->len);
  printf("msg->allocated_len = %u \n", (size_t) msg->allocated_len);
  return 0;
}

So it prints out:

msg->str = [this is my message] 
msg->len = 19 
msg->allocated_len = 512

The only strange is why the allocated_len is 512 instead of 256. Thanks to everyone for the reply...

Answer 3

Resurrection, debugging led me to the next solution. Thank you Hasturkun for your help, I wanted to post my answer since yesterday but new members cannot answer their questions before 8 hours pass. The solution is this:

int main(void)
{
  GString *msg = NULL;
  gchar *p;
  gchar buf[256];

  msg = g_string_sized_new(256);
  printf ("Enter a message (255 characters at most): ");
  p = fgets(buf, sizeof(buf), stdin);
  g_string_assign(msg, buf);
  printf("msg->str = [%s] \n", (char *) msg->str);
  printf("msg->len = %u \n", (size_t) msg->len);
  printf("msg->allocated_len = %u \n", (size_t) msg->allocated_len);
} 

And it prints out everything very well... Thank you all for your comments!