How to get length of an array that is filled with input

Question

I have asked a question here and now the code below makes the work that I expected (the work that I mentioned previously). Now I have another issue: if I write tmp[20] and if the size of the input is 20 chars, the code works. However the size of the input is not known. Therefore, there can be a maxsize, but the actual size depends on the input. How can I make this code work with every length? (yes, the code works when I write 200 inside of tmp but the size of 'message' depends on the whole array. It should be 3 chars before end and 6 chars after start).Therefore when I write 200 inside of tmp[] and the input is shorter than 200 chars, the message returns incorrectly. I think I should use dynamic memory allocation but I could not implement it to my code.

Here is my complete code:

char tmp[20] = { 0 };
int len = sizeof(tmp) / sizeof(tmp[0]);
String pack;
String command;
String Size;
String messum;
String message;
String checksum;

int Index = 0;
bool Seen = false;

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

void loop() {  
    while (Serial.available() > 0) {
        char received = Serial.read();

        if (received == '!') {
            Seen = true;
        } else
        if (received == '#') {
            return strdup(tmp);
        } else
        if (Seen == true) { 
            if (Index < 2) {
                //Serial.print("P");
                pack = tmp[Index++] = received;
                Serial.print(pack);
            } else
            if (Index < 4) {
                //Serial.print("C");
                command = tmp[Index++] = received;
                Serial.print(command);
            } else
            if (Index < 6) {
                //Serial.print("S");
                Size = tmp[Index++] = received;
                Serial.print(Size);
            } else
            if (Index < (len - 3)) {
                //Serial.print("M");
                message = tmp[Index++] = received;
                Serial.print(message);
            } else
            if (Index < len) {
                //Serial.print("C");
                checksum = tmp[Index++] = received;
                Serial.print(checksum);
            }  
        }
    }
    return NULL;
    //input:  asdeyh134!123456789abcdefghtry#8647dfn
}

I can use but I could not implement it to my code. I am quite beginner — ReduX Completedy, Apr 11 '20 at 14:44
You must still fix the error `return strdup(tmp);` as `loop` is `void`. — Paul Ogilvie, Apr 11 '20 at 14:44
It is not an error when I delete that part the output does not stop when # is seen — ReduX Completedy, Apr 11 '20 at 14:45
There are plenty of examples online ([here](https://www.educative.io/edpresso/how-to-use-malloc-in-c)) and on SO, as for instance [this](https://stackoverflow.com/questions/41830461/allocating-string-with-malloc), ... — CRM, Apr 11 '20 at 14:47
Since your array is going to contain character strings, then just keep the string null terminated by always writing a 0 to the next spot when you add a character. Then you can use strlen to get the length of the string in the array. It will count up to that null character. — Delta_G, Apr 11 '20 at 16:29
Anywhere you write any character to the end of your string. Then the next line should write 0 to the next slot of the array. Can you identify the lines in your code that write values into your array? — Delta_G, Apr 11 '20 at 17:56

score 0 · Answer 1 · answered Apr 11 '20 at 17:58

0

Anywhere you are adding characters to your array like this:

if (Seen == true) { 
            if (Index < 2) {
                //Serial.print("P");
                pack = tmp[Index++] = received;
                Serial.print(pack);

You should also null terminate your string like so:

if (Seen == true) { 
            if (Index < 2) {
                //Serial.print("P");
                pack = tmp[Index++] = received;
                tmp[Index] = 0;
                Serial.print(pack);

That way you can use strlen to get the length of the string in the array. It will count the number of characters up to that null character.

int length = strlen(tmp);

On the next pass of the loop when you write in another character you will write it over that null and then write a new null right after that new character.

answered Apr 11 '20 at 17:58

Delta_G

2,927
2
9
15

the output become P1P2C3C4S5S6S7S8S9SaSbScSdSeSfSgShStSrSySaSsSdSaSsSdSaSsSdS – ReduX Completedy Apr 11 '20 at 19:19
It should be M's and C's but I think the code did not reach that part. Also it did not stop when # is recieved – ReduX Completedy Apr 11 '20 at 19:20
asdasd!123456789abcdefghtry#asdasdasd this was the input – ReduX Completedy Apr 11 '20 at 19:21
the input was asdasd!123456789abcdefghtry#asdasdasd and the output is P1P2C3C4S5S6 please ignore my first comment – ReduX Completedy Apr 11 '20 at 19:28
I don't know what the code that produced that output looks like. – Delta_G Apr 12 '20 at 01:00
That output looks like it is also printing the characters that are commented out in the code above in between printing the received characters. Since you don't actually print the contents of the array anywhere in the code you can't really comment on what you think is in it. – Delta_G Apr 12 '20 at 01:01
I added these chracter to understand if the code reaches that part or not. When I delete them the output is nor change it becomes 123456 – ReduX Completedy Apr 12 '20 at 10:38
Isn't that the output you wanted? You wanted what starts at the ! right? – Delta_G Apr 12 '20 at 16:27
I still don't know what the code looks like that is producing the current output (HINT HINT!) – Delta_G Apr 12 '20 at 16:28
the last part of my code should return 3 chars befor e# and the previous if else part should return the 6 chars after! and 3 chars before the # – ReduX Completedy Apr 12 '20 at 16:48
OK, nevermind then. I was trying to see the new version of your code and keep helping you. I guess that's not what you want. – Delta_G Apr 12 '20 at 16:58
Can I get your e mail? – ReduX Completedy Apr 13 '20 at 23:34
Absolutely not. Why would I do that? – Delta_G Apr 14 '20 at 00:00

How to get length of an array that is filled with input

1 Answers1