not getting expected output from fgets() function

Question

Here simple code I am not getting the expected output.

#include<stdio.h>

int main()
{
   char buf[1024];
   while(1)
   {
      fgets(buf,strlen(buf),stdin);
      printf("%s",buf);
      printf("hello");
   }
}

In the above code I am want whatever the string I enter from keyboard to be printed out to me the same and then hello. As I know fgets() is a blocking function till I input a string from keyboard and press ENTER it will block the program till that time. So when I run it I expect it as follows

$ ./a.out
I input some text here <ENTER>
I input some text here 
hello

But actually what I am getting output is infinite loop of "hello" printed on terminal. Why my fgets() not blocking the program? Any idea?

Answer 1

The problem is strlen(buf) is return 0 because buf[0] just happened to be 0 (not guaranteed). You should use sizeof(buf) instead:

fgets(buf,sizeof(buf),stdin);