Unable to read data from serial port in C on Ubuntu - c

Question

I have two C Programs 1. To Write Data to Serial Port and 2. To Read Data from Serial Port. I have connected a USB-Serial converter to my laptop and shorted Tx & Rx to test the program.
Program 1 is getting executed successfully.
Program 2 blocks at read.
Can anyone please suggest a solution for this.
Thanks in advance.
Program to Write to Serial Port:
#include <stdio.h> /* Standard input/output definitions */
#include <string.h> /* String function definitions */
#include <unistd.h> /* UNIX standard function definitions */
#include <fcntl.h> /* File control definitions */
#include <errno.h> /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */
/*
* 'open_port()' - Open serial port 1.
*
* Returns the file descriptor on success or -1 on error.
*/
int write_port(void)
{
int fd; /* File descriptor for the port */
fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1)
{
/* Could not open the port. */
perror("open_port: Unable to open /dev/ttyUSB0 - ");
}
else
fcntl(fd, F_SETFL, 0);
int n = write(fd, "ATZ\r", 4);
if (n < 0)
fputs("write() of 4 bytes failed!\n", stderr);
return (fd);
}
void main(){
printf("\nAccessing Serial Port to Write\n");
int fd=write_port();
if(fd<0){
printf("\nSerial Port Access Failed\n");
return;
}
printf("\n%d\tSuccess\n",fd);
}
Program to Read from Serial Port:
#include <stdio.h> /* Standard input/output definitions */
#include <string.h> /* String function definitions */
#include <unistd.h> /* UNIX standard function definitions */
#include <fcntl.h> /* File control definitions */
#include <errno.h> /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */
/*
* 'read_port()' - Reads serial port 1.
*
* Returns the file descriptor on success or -1 on error.
*/
int read_port(void)
{
int fd = open("/dev/ttyUSB0", O_RDONLY | O_NOCTTY);
if (fd == -1)
{
/* Could not open the port. */
perror("open_port: Unable to open /dev/ttyUSB0 - ");
}
char buffer[32];
int n = read(fd, buffer, sizeof(buffer));
if (n < 0)
fputs("read failed!\n", stderr);
return (fd);
}
void main(){
printf("\nAccessing Serial Port to Read\n");
int fd=read_port();
if(fd<0){
printf("\nSerial Port Access Failed\n");
return;
}
printf("\n%d\tSuccess\n",fd);
}