Thread: auto detect com ports using c

Hello everyone,
Is there any way i can list the number of active com ports in my system using c,i have tried searching for it in msdn but there there is no code example for it in c

If anyone has any idea pls share!!

Originally Posted by grumpy

Yes, there are solutions, but what you're asking about is outside the scope of C. You need to read relevant documentation for your host (operating system, etc), since the solutions are system dependent.

I am currently working on Windows 7 professional (32bit),compiler: gcc(codeblocks)
Can you point me to the relevant document you mentioned.

This is what i have got so far.I'm sure there must be a more efficient way of doing this

Code:

#include <stdio.h>
#include <windows.h>
#include <string.h>
int main()
{
    char port[] = "COM1";
    char port1[] = "\\\\\.\\";
    strcat(port1,port);
    int i = 0,j=49,k = 49;
    HANDLE hSerial;
    for(i = 0; i<=10; i++)
    {
        hSerial = CreateFile(port1, GENERIC_READ | GENERIC_WRITE,0,0,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0);
        if(hSerial==INVALID_HANDLE_VALUE)
        {
            if(GetLastError()==ERROR_FILE_NOT_FOUND)
            {
                //printf("\nError:Serial Port does not exist.");
                //printf("Sub Error: ERROR_FILE_NOT_FOUND");
                ;
            }
            //printf("\nSerial port communication error.\nSub Error: INVALID_HANDLE_VALUE");
            printf("Detecting port...");
            port1[strlen(port1)-1] = j;
            j++;
            if(j > 58)
            {
                printf("\nAuto Detect feature is enabled only for COM1 to COM9\n");
                break;
            }
            printf("%s\n",port1);
            ///End of Code for opening port
            //system("pause");
        }
        else
        {
            printf("Port opened.\n");
            break;
        }
    }
    return 0;
}

After some trying i was able to figure out a way of doing it.Quiet simply actually,nothing fancy.
Any advice on improving it are welcome.

Code:

#if AUTO_COM
    printf("Detecting port...\n");
    Sleep(500);
    while(k < 258)  //0 to 256
    {
        hSerial = CreateFile(port, GENERIC_READ | GENERIC_WRITE,0,0,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0);
        if(hSerial==INVALID_HANDLE_VALUE)
        {
            if(GetLastError()==ERROR_FILE_NOT_FOUND)
            {
                com_check_flag = 1;
            }
            com_check_flag = 1;
        }
        else
        {
            com_check_flag = 0;
            printf("Detected port:  COM%d\n",k-1);
            Sleep(800);
        }
        if(com_check_flag == 1)
        {
            sprintf(port,"\\\\\.\\com%d",k);
            k++;
        }
        if(k > 257)
        {
            printf("Unable to detect port.\n");
            CloseHandle(hSerial);
            system("pause");
            exit(1);
        }
        if(com_check_flag == 0)
        {
            break;
        }
    }
#endif

hSerial is a HANDLE by the way.

Originally Posted by grumpy

You're suggesting that you can't simplify this?

Code:

            if(GetLastError()==ERROR_FILE_NOT_FOUND)
            {
                com_check_flag = 1;
            }
            com_check_flag = 1;

I'd suggest giving your variables more descriptive names. A name 'k' is not exactly informative.

Better not to use system() to implement a pause. There are plenty of ways to wait for user input without using a system call, that only involve one or two lines of code. Using a system call, in this case, has no justification apart from laziness and unwillingness to find practical alternatives.

Windows usually only supports com ports COM1 through COM9.

There is no need for the Sleep() calls.

The loop logic, to say the least, is rather contorted. Try rewriting to avoid using the break keyword (or any other covert goto).

Hello Mr. grupmy,
*'k',in this case is a simple counter with a range of 0 to 257,changed its name y the way .
*And i have been meaning to ask,when is it useful to use system() calls and when is it not?The reason why i used system("pause") here is because if my .exe file is out of my projects folder,and when the condition is met,the cmd window closes down before the user can view the error message.I can get the same function using getch() as well.
*Com1 to com256 are supported in windows.To be able to access ports above com9,we need to add the "\\.\" before the comx port.(eg:\\.\com13).Found these details on msdn.
* I used Sleep here as a kind of delay sequence.So that the user knows which port has been assigned/used.If there is a better way,please let me know.
*The only way i can think of avoiding break is by checking the true condition in the while.

Code:

int com_check_flag  = 3; //something other than 0 or 1.
while(k < 258 && com_check_flag != 0)  //0 to 256

awaiting your reply..