Thread: How to verify my incoming UDP packet correctly?

unknown_072: Your code in #11 still uses "+" for string concatenation. That does not work as laserlight mentioned in post #2. That needs to be fixed.

Structure: There's no need to reinvent the wheel. Your "compare" function in #5 can be simplified to something like this:

Code:

int compare(const char *string1, const char *string2) {
    return strcmp(string1, string2) == 0;
}

(I also added "const" to the parameters which you forgot to do.)

Originally Posted by christop

unknown_072: Your code in #11 still uses "+" for string concatenation. That does not work as laserlight mentioned in post #2. That needs to be fixed.

Structure: There's no need to reinvent the wheel. Your "compare" function in #5 can be simplified to something like this:

Code:

int compare(const char *string1, const char *string2) {
    return strcmp(string1, string2) == 0;
}

(I also added "const" to the parameters which you forgot to do.)

I checked how to use strcat, but here also, I'm not sure how to read the PacketBuffer, I just want to verify if the 3 digits of the string that is received on the UDP packet are the same as tableID;

Code:

if (packetBuffer, strcat(str1, str2)

Structure:
I've rewinded my code back to basic, thought it was helpful to share a bit more code.

So monday I'll work on this again, first thing, since I really want to finish this piece of code.
It's clear to me that the "+" does not work like this in C. Hopefully I can work this out with your help.

Once again, I'm trying to simply read only the first 3 digits of the udp packet and want to compare them to the variable 'tableID'

Thanks so far!

Originally Posted by Structure

I can understand this, but why include an entire library for one function?

You're already linking to libc, right? Then you have all of the string functions.

Although i used strlen, i'm saying it could be useful sometimes to create the one function you need.

Sure, it can be useful as an academic exercise, but (IMO) it's pointless if you just want to write an application. Just use existing functions in libc. They're likely better tested and optimized than something you write yourself. Less code means less to debug.

Hi laserlight,

Thank you!
So I've changed my code:

I've declared expected

Code:

      snprintf(expected, sizeof(expected), "%u_available", (unsigned int)tableID);
      
      if (strcmp(packetBuffer, expected) == 0) {
        modeAvailable();
        Serial.println("This works!");
      }

and declared expected;

Code:

char expected[14]; // NNN_available

And when I upload this I do recieve the message, but it won't return true since I'm not seeing the Serial Print "This Works!"

This is what I'm seeing in my monitor when sending the packet:

08:02:05.419 -> Received packet of size 13
08:02:05.419 -> From 10.168.1.100, port 9101
08:02:05.419 -> Command: 101_available
08:02:05.454 -> --END--

All correct information.
But still it won't return true

Originally Posted by laserlight

Okay. Temporarily change this:

Code:

if (strcmp(packetBuffer, expected) == 0) {
  modeAvailable();
  Serial.println("This works!");
}

to this:

Code:

if (strcmp(packetBuffer, "101_available") == 0) {
  modeAvailable();
  Serial.println("This works!");
}

Compile and run your code with exactly the same test input. Do you get "This works!" as the actual output?

If the answer is yes, then it implies that there's still something wrong with how you're constructing the string. So, one place to start is to insert this before you do the string comparison and see what you get:

Code:

Serial.println(expected);

If the answer is no, then it implies that there's something else wrong, i.e., some other change you made has made your code become incorrect in between the time you wrote that "I'm sure the message arrives correctly, for debug I did a simple string comparison`!strcmp(packetBuffer, "101_available"));`, which works" in post #1 and now.

Okay so I've tested this, and yes it works.

09:28:03.457 -> Received packet of size 13
09:28:03.457 -> From 10.168.1.100, port 9101
09:28:03.457 -> Command: 101_available
09:28:03.457 -> --END--
09:28:03.457 ->
09:28:03.457 -> Confirmed
09:28:03.457 -> This works!


If I add:

Code:

Serial.println(expected);

Nothing is printed, it is a loop so it should print constant

Originally Posted by laserlight

I wrote a quick program to check that I didn't make some silly mistake:

Code:

#include <stdio.h>

int main(void)
{
    unsigned char tableID = 101;
    char expected[14]; // NNN_available
    snprintf(expected, sizeof(expected), "%u_available", (unsigned int)tableID);
    printf("%s\n", expected);
    return 0;
}

Compiling and running the above program results in this output, which is exactly what I expected:

Code:

101_available

Therefore, what you have described is impossible (unless there is undefined behaviour elsewhere): there can be no value of tableID that will result in expected being an empty string.

To confirm, are you saying that you wrote this:

Code:

char expected[14]; // NNN_available
snprintf(expected, sizeof(expected), "%u_available", (unsigned int)tableID);
Serial.println(expected);
if (strcmp(packetBuffer, expected) == 0) {
    modeAvailable();
    Serial.println("This works!");
}

and it didn't print anything where Serial.println(expected) was supposed to print something?

This actually works now! I do have to clean up a bit but this my result from the serial monitor.

Code:

11:12:19.369 -> Received packet of size 13
11:12:19.369 -> From 10.168.1.100, port 9101
11:12:19.369 -> Command: 215_available
11:12:19.404 -> --END--
11:12:19.404 -> 215_available
11:12:19.404 -> Confirmed
11:12:19.404 -> This works!
11:12:19.404 -> Expected: 215_available


11:12:25.782 -> Received packet of size 13
11:12:25.782 -> From 10.168.1.100, port 9101
11:12:25.782 -> Command: 101_available
11:12:25.782 -> --END--
11:12:25.782 -> 215_available

So, the tableID is currently 215, which is correct.
With the 101_available it does print 'Expected' which obviously is correct when you look at the code, it's printing what it expects.

This is what I have;

Code:

        snprintf(expected, sizeof(expected), "%u_available", (unsigned int)tableID);
        Serial.println(expected);
          if (strcmp(packetBuffer, expected) == 0) 
          {
            modeAvailable();
            Serial.println("This works!");
            Serial.print("Expected: ");
            Serial.println(expected);
            
          }

I do think this did the trick, I'll work my code out today to see if it works as supposed with all the functions.

Really thanks for all the help! I'm happy now!