read file descriptor HANGS - c++

Question

I have a very simple source reading file descriptor which hangs.
Could anyone notice the problem the code has?
The first one is the problematic source and the second one is the working source found on the web. Two sources are almost identical.
First source
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
int main(int argc, char ** argv) {
int n, in;
char buf[1024];
if ((in = open(argv[1], O_RDONLY)<0)) {
perror(argv[1]);
return -1;
}
while((n = read(in, buf, sizeof(buf))) > 0 ) { //HANGS at THIS LINE!!!!!!!!!!!
printf("TEST\n");
}
close(in);
return 0;
}
Second Working source got from online
/*
* ============================================================================
* Name : sp_linux_copy.c
* Author : Marko Martinović
* Description : Copy input file into output file
* ============================================================================
**/
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>
#define BUF_SIZE 8192
int main(int argc, char* argv[]) {
int input_fd; /* Input and output file descriptors */
ssize_t ret_in; /* Number of bytes returned by read() and write() */
char buffer[BUF_SIZE]; /* Character buffer */
/* Create input file descriptor */
input_fd = open (argv [1], O_RDONLY);
if (input_fd == -1) {
perror ("open");
return 2;
}
/* Copy process */
while((ret_in = read (input_fd, &buffer, BUF_SIZE)) > 0){
printf("TEST\n");
}
/* Close file descriptors */
close (input_fd);
}

Answer 1

By a funny coincidence, you are reading from stdin. This is because in your if(in = ... you misplaced some brackets.
What is happening is that first open(argv[1], O_RDONLY)<0 gets evaluated, and the result gets put into in. Since the result of open() is not smaller than zero (on succesfull open), in becomes 0. And stdin is the name for the filedescriptor which is zero (on most systems). So it is a valid file descriptor, and read is very happy to read from it. It is just not getting any, until you type something in your console.
quick fix:
if ( (in = open(argv[1], O_RDONLY)) < 0) {