Reading Serial Port Data

Question

I am trying to read in serial port data in C on Mac OS. Configuration of serial port is done in separate Arduino IDE.

I am able to read partial data, but then the printed data repeats itself and starts reading zeros as seen below. If I remove O_NONBLOCK, the program just hangs. What can I do to fix this problem? Secondly, given that I am reading in data in a for loop, how do I make sure the read rate corresponds with the baud rate?

Seen data: 296 310 0

320 295 311

320 295 311

9 296 311

320 295 311

320 295 311

9 296 311

...

0 0 0

0 0 0

0 0 0 etc.

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>

int buffer[300];

int main(int argc, const char* argv[])
{

    // open serial port
    int port;
    port = open("/dev/tty.usbmodem1411", O_RDONLY | O_NONBLOCK);
    if (port == -1)
    {
        printf("Unable to open serial port.\n");
        return 1;
    }

    // instantiate file
    FILE* file = fdopen(port, "r");
    if (file == NULL)
    {
        printf("Unable to instantiate file.\n");
        close(port);
        return 2;
    }

    for (int j = 0; j < 200; j++)
    {

        fscanf(file, "%d %d %d", &buffer[3*i], &buffer[3*i+1], &buffer[3*i+2]);
        printf("%d %d %d\n", buffer[3*i], buffer[3*i+1], buffer[3*i+2]);

        i = (i + 1) % 100;

        usleep(10000);

    }

    fclose(file);
    close(port);

    return 0;

}

Answer 1

For Chris Stratton:

if (fgets(temp, sizeof(temp), file) != NULL) 
{ 
     sscanf(temp, "%d %d %d\n", &buffer[3*i], &buffer[3*i+1], &buffer[3*i+2]); 
     printf("%d %d %d\n", buffer[3*i], buffer[3*i+1], buffer[3*i+2]); 
}

However, going back to my original question, even if I'm using fscanf and printf, I obtain data, and then I only read zeros indefinitely. I'm thinking this might be more of a serial port communication issue?