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bogdan » simple windows COM port logger

03:30 pm on Dec 20, 2011 | read the article | tags:

yesterday, i’ve posted my wrapper library for the windows COM port with the promise of posting the actual C program that uses it. to compile it you need mingw (see here my tutorial on how to get it up and running). the program is simple and writes in the text.txt file whatever it receives on the serial interface, but no more than MAXLINES lines (in this case, 10 lines). you need to save the previous code as “serial.h” in the same directory as the code below. then, compile it and that’s it! =)

ask whatever questions here, and i will answer.

#include <stdio.h>
#include <windows.h>
#include "serial.h"
// the number of lines read from the serial interface.
// good for data acquisition for a specified amount of time.
#define MAXLINES 10

int main (int argc, int ** argv) {
    HANDLE comPort;
    FILE * f;
    char buffer[32];
    unsigned short int readbits = 0;
    unsigned long int lines = 0;
    unsigned short int c;

    // my COM port is COM15. be sure to change it accordingly
    if ((comPort = openSerialConsole("\\\\.\\COM15")) == (void *) NULL) {
        printf ("Error: COM Port!\n");
        return 1;

    // open the file "text.txt". change it for a different file
    f = fopen ("test.txt", "w+");

    // read online MAXLINES lines
    while (lines < MAXLINES) {
        // readbits is the number of bytes read from the COM port
        while ((readbits = readFromSerialConsole(comPort, buffer, 32)) != 0) {
            // a good thing to check that the readbits+1 character marks the end
            // of the string. saves you from "Segmentation fault!" errors
            buffer[readbits] = 0;

            // check buffer for ENDL character
            for (c = 0; c<readbits; c++)
                if (buffer[c] == '\n') {
                    if (lines == MAXLINES) buffer[c] = 0;

            // output to the standard IO, and
            printf("%s", buffer);
            // to the file
            fprintf(f, "%s", buffer);

    // close the file handle
    fclose (f);

    // close the COM port

    return 0;

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