Concatenate two char arrays (for udp client)

Other Hardware Sensors
1

I'm using Arduino as a UDP client to send information about values read from sensors.

I'd like to send packets like:

"string1=value1"

where value1 is an integer read from Arduino analog pins.
The problem is that udp.write() only takes as parameter char arrays, so i can't sum a string to an integer and then pass the new string to udp.write().

I have to concatenate a char array to an integer value and then pass the array to the udp.write() function.

At the moment, i'm using dtostrf(FrontSonar_Reading,1,2,temp);
in order to save the integer value in the "temp" array char, but i do not know how to concatenate this result to the array char.

Actually, I have something like:

char string1[] = "string1=";

void loop(){
  //...
  dtostrf(FrontSonar_Reading,1,2,temp);
  Udp.beginPacket(remoteIp, remotePort);

   Udp.write(string1);
   Udp.write(temp);

   Udp.endPacket();
}

it works, but it sends two packets; i'd like to send just one packet with the string and the integer at the same time.

Is it possible?

2

I'm not sure this is the best way to do it when you use UDP but sprintf works in all cases.
Below is a sketch that concatenates a string "=" a value.

void setup() {
  Serial.begin(115200);
}

void loop() {

    char myConcatenation[80];
    char myCharArray[16]="A variable name";
    int myInt=5;
    sprintf(myConcatenation,"%s = %i",myCharArray,myInt);
    Serial.println(myConcatenation);
    delay(100);
}

look at this link for more info on sprintf http://www.cplusplus.com/reference/clibrary/cstdio/sprintf/
I hope this helps
Best regards
Jantje

3

Thanks a lot for your suggestion!

Is sprintf() safe? Can it have memory lacks or problems?

I'd like to build a roboust application and i'm trying to avoid memory problems.

What do you think about this?

Thanks again.

4

Can this function be more safer than sprintf()?

char * BufferInsertStringValue(char * s,int startingPosition, char * command) {
  int i = 0;
  int stringLength=strlen(s)-1;
  for ( i = 0;i <= stringLength;i++) {
    command[startingPosition + i - 1] = s[i];
     }
  command[startingPosition + i] = '\0';
  return command;
}

where s is the temp array char and comando is the original text string which i want to concatenate with the integer value.
I call this function with:

char * vett;
vett = BufferInsertStringValue(temp, 14, sonar_center);

Do you think it's safer than sprintf function?

5

The only risk you have with sprintf is that you will outrun your target buffer space.
As you are using a char buffer containing the variable name and you are adding a int you can 100% guarantee your buffer is big enough.
Unless you go for runtime memory allocation (like String class does) you will always have this problem.
Best regards
Jantje

6

Hello Friends, I am exploring the below sketch to concatenate arrays.. If I want to add "%" symbol to the end of the integer value to myConcatenation[80] array, how do I do it? basically, when I print myConcatenation, I would like to see the output as "A variable name = 5 %.

Any guidance is appreciated.

void setup() {
  Serial.begin(115200);
}

void loop() {

    char myConcatenation[80];
    char myCharArray[16]="A variable name";
    int myInt=5;
    sprintf(myConcatenation,"%s = %i",myCharArray,myInt);
    Serial.println(myConcatenation);
    delay(100);
}
7

Ok. Figured it out myself with below code. Is there any other better way to achieve it?

void setup() {
  Serial.begin(9600);
}

void loop() {

    char myConcatenation[80];
    char myCharArray[]="A variable name";
    int myInt=5;
    char myStr[] = "%";
    sprintf(myConcatenation,"%s = %i %s",myCharArray,myInt,myStr);
    Serial.println(myConcatenation);
    delay(100);
}
8

Lavan:
Is there any other better way to achieve it?

Reading the sprintf documentation? ]:smiley:
You probably need to add a \ before the % but I'm sure google can point you to documentation of the printf family that tells you how to do it.

9

Thanks for your direction. Got the answer from the printf statement guide. Below one does the trick.

sprintf(myConcatenation,"%s = %i%%",myCharArray,myInt)
10

great :slight_smile:
So % is the escape character and not . Makes sense.
Best regards
Jantje