read() file no response?

gistfile1.md

NG

if (fd = open("test.txt", O_RDONLY) == -1) {
  printf("open error\n");
}
read(fd, buf, size); // No response?(fd == 0)

---

OK

if ((fd = open("test.txt", O_RDONLY)) == -1) {
  printf("open error\n");
}
read(fd, buf, size);