Read /dev/ttyUSB0 with a c program on LINUX - c

Question

I want to read data frames sent by a GPS XBee protocol. The USB XStick receives the following data:
CHARS : 15931 SENTENCES = 0 CHECKSUM : 58
Heading : 55 Tilt: -46 Roll:2
CHARS : ....
and so on ... I can read by typing in the terminal control :
$ screen /dev/ttyUSB0
I'd like to see these details in the same way, but with a program written in C. Here's what I do :
#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <sys/fcntl.h>
#include <unistd.h>
#include "serial_port.h"
void read_Serial_Port(const char* DEVICE_PORT)
{
int file;
struct termios options;
char message[100];
unsigned int nCountMax = 60;
bool b;
file = open(DEVICE_PORT, O_RDONLY | O_NOCTTY | O_NDELAY);
if(file == -1){perror("Unable to open the serial port\n");}
printf("Serial port open successful\n");
tcgetattr(file, &options);
cfsetispeed(&options, B9600);
cfsetospeed(&options, B9600);
options.c_cflag |= (CLOCAL | CREAD);
options.c_cflag |= PARENB; //No parity
options.c_cflag |= PARODD;
options.c_cflag &= ~CSTOPB;
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8; //8 bits
options.c_iflag |= (INPCK | ISTRIP);
tcsetattr(file, TCSANOW, &options);
fcntl(file, F_SETFL, FNDELAY);
printf("Reading serial port ...\n\n");
b = readMessage(file, message, nCountMax);
if (b == 0){printf("Error while reading serial port\n");}
else printf("Serial port read successful\n");
close(file);
printf("Serial port closed\n");
};
bool readMessage(int file, char *message, unsigned int nCountMax)
{
int nbCharToRead;
char data[100];
int i;
if (file != 0)
{
i = 0;
while (i<nCountMax && data != ".")
{
if (read(file,&data,1) == -1)
{
printf("reception error\n");
return false;
}
else
{
message[i] = *data;
printf("%c", message[i]);
i++;
}
}
message[i] = 0;
return true;
}
}
But it does not work, I get "reception error", corresponding to:
read(file,&data,1) == -1
Where am I going wrong?
My program is the following:
bool readMessage(int file, unsigned int nCountMax)
{
int i;
size_t nbytes;
ssize_t bytes_read;
if (file != -1)
{
i = 0;
char message[100];
char data[100];
while (i<nCountMax && data != ".")
{
if (read(file, data, 1) == -1)
{
printf("reception error\n");
printf("code errno = %d\n", errno);
return false;
}
else
{
nbytes = sizeof(data);
bytes_read = read(file, data, nbytes);
message[i] = *data;
printf("%c", message[i]);
i++;
}
}
message[i] = 0;
return true;
}
}
This time there are no more errors, but the characters shown are wrong:
$$$$QUC
U$C
$$$$JQMJ' J$Cz(HSQ'Q'y
UKUNiQUMJ
the dollar signs $$$$ represent numbers in groups of four... I repeat that what I would like to have is
CHARS : 15931 SENTENCES = 0 CHECKSUM : 58
Heading : 55 Tilt: -46 Roll:2
CHARS : .....
I have tried using %c, %d, %x in the format string, but obviously none of them worked properly ...
Thank you!

Answer 1

In my code, I only change c_cflag, as follows:
// Enable the receiver and set local mode...
options.c_cflag |= (CLOCAL | CREAD);
// Set 8-bit mode
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8;
I'll post more code tomorrow, but give that a shot (and don't modify c_iflag).