Questions tagged [pointer]

A variable in C/C++ which stores the type and location of data in memory.

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19 views

I can't receive string that I have sent through nrf correctly

I'm using arduino uno and nrf24l01. to monitor sensor data. But this is the message that master receives: ⸮ this is my slave code. void monitoring() { delay(10); radio.stopListening(); ...
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1answer
20 views

Calling functions from an array of pointers in a library causes 'undefined reference to' error

I am trying to create a library, where I have an array of pointers to functions in it. This array is used by other functions in the library. This is the code of the header file: class Lib { public: ...
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4answers
103 views

How do arrays work?

It's been days now I'm trying to figure out how arrays work in Arduino IDE. For better understanding, I assembled some pieces of code I found here and there to write this sketch: #define arrayLength(...
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119 views

No known conversion for argument 1 from 'Object*' to 'int*'

I'm terrible with pointers and need help passing an object to a library I'm writing. I'm getting the error no known conversion for argument 1 from 'LCDMenuItem*' to 'int*' when I try to compile. How ...
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1answer
57 views

typedef function pointer array declaration problem

Thanks for all your feedback. It helped. I rewrote this yet another time and this time it works perfectly. I included three variations: a simple example using an array of function pointers, a Lambda ...
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1answer
32 views

Update `char* `

I have a class containing few char* variables: char* msgTopic = "myHome/MSGS"; char* groupTopic = "myHome/All"; char* errorTopic = "myHome/Err"; but, I wish to have it defined outside the ...
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1answer
46 views

writting to buffer from serial input

Can some one explain this behaviour please, i have the following code byte buffer[512]; byte block; byte len; Serial.setTimeout(60000L) ; // wait until 20 seconds for input from serial ...
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1answer
53 views

Problem with passing string pointer from child to parent

I am trying to pass a pointer to a const char * from a child to its parent, but I am clearly not understanding how to do this correctly. Here is the code which contains three classes: 1) parent 2) ...
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1answer
34 views

Having an issue accessing values from a pointer

Context This may be more of a C++ question than an arduino specific question, but it's dealing with arduino c++ so I thought I'd start here. I'm building a class to abstract some simple melody ...
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2answers
119 views

Compute SHA256 of string and output to string

In my Arduino project I want to compute the SHA256 hash of a string and store the result to a string, and do this recursively many times (i.e. compute hash of hash of hash etc...). So my goal is to ...
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1answer
40 views

Programfault when dereferencing a 64bit int on due

I am running into a strange behaviour with my code. The following works without problems on an Arduino Nano but it seems to crash on a DUE void putData64(byte* packet, int pos, uint64_t data) { ...
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1answer
289 views

ArduinoJSON v6 - Passing buffer as function parameter

I'm new to ArduinoJSON - so perhaps it is a newbie's question.... but I wish to pass a StaticJsonDocument into a function as a parameter ( later on it should be implemented in a library ). exmaple ...
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1answer
67 views

Parsing array of an object in a library constructor

I am trying to develop an Arduino library that consists out of two classes. I want 'WayPointStack' to store an array of 'WPCommand', but I can't get it to work. WayPointStack.h #ifndef ...
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1answer
324 views

Passing arrays, global arrays within functions, pointers, and declaring array sizes

I'm super confused right about now! I've been working on project involving Xbees in API mode, and I need to send different arrays of bytes to the Xbee depending on which buttons I press. Mostly what ...
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0answers
70 views

Using pointer to a Global function

I am trying to store and use a pointer to a global function. The function global_f returns a String and takes an object as parameter: String global_f(Request r){ // ... return "This is it"; } ...
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47 views

Losing value of variable

I am making a project involving the AutoConnect, ArduinoJSOn and LedControl libraries to fetch some values from an endpoint. Basically what I do is connect to the internet, fetch the values from a ...
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2answers
136 views

Creating an array of structures which store bitmaps to work with u8glib

I've tried reading the documentations and I'm getting desperate because I can't find anything. I need to create an array of structures, which contains a bitmap stored in PROGMEM space (because of ...
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1answer
78 views

Dynamically modifying the call stack using pointers

In a C++ Arduino library, can we modify the call stack from inside a function by intentionally decrementing a pointer to a stack variable so that it's out of range? Like this: void FooBar() { char ...
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1answer
49 views

Dynamic allocation/ Pointer to Pointer to update an Array containing parameter [closed]

topicArray defined as follows: const char* msgTopic = "Home/Messages"; const char* groupTopic = "Home/All"; char* deviceName = deviceTopic; const char* topicArry[2] = {deviceTopic, groupTopic}; But ...
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0answers
274 views

Is there any working analogue to the pair std::function and std::bind in Arduino?

Both ArduinoSTL and StandardCplusplus don't support them. They implement the version that is compatible with c++03 (not c++11). This functionality is handy when you design libraries that work with ...
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1answer
46 views

Message Interpreter and Handler - How to store a function name in a struct?

For a project, I need to store an array of structures in PROGMEM. Array MessageTable[] will be composed of about ten struct InMessage elements. InMessage looks sort of like this: struct AvcInMessage {...
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1answer
140 views

Initialize and read from a PROGMEM array of pointers to PROGMEM arrays

I'm working on a project for the arduino uno for which I need multiple constant arrays of bytes. Such an array is initialized like so: const byte charR[] PROGMEM = { B01111111,//top half ...
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1answer
341 views

Sketch with multiple classes (.h and .cpp) - how to interconnect classes

I wanted to move most functionality of my sketch into different classes, to keep things better organized. One class worked just fine, but when I had to use multiple classes and pass information ...
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0answers
82 views

Storing an array of objects

I followed the instructions of this post: Storing an array of function pointers. To show my problem I shorted my code extremely but the problem is still there. My classes are defined as followes: ...
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2answers
329 views

passing arrays via function returns wrong values [closed]

I am trying to use the values of an array in some other function, but when I return via a function the contents is wrong. This is the external function file I'm trying to use #include "Arrayreturner....
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1answer
323 views

Pointer memory allocation in function

I would like to know how Arduino allocate memory for pointers in function arguments. For instance. I have this code that use 192 bytes (Arduino IDE compiler: Global variables use 192 bytes (9%) of ...
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1answer
35 views

Runtime Error when using array of structs of unknown size as variable within class - some kind of overflow issue?

I have a class defined as below, it's basically a simple ring buffer, with some methods for getting useful statistics from the data held in the buffer. enum BalanceMsgType{ BAL_MSG_NOT = 0, ...
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1answer
325 views

Assigning Pointers to arrays - incorrect results?

I'm trying to build a transmission frame for a workshop library for the Arduino Uno. I have the byte frame inside an array, give it to another function that builds a bit frame and then want to ...
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1answer
626 views

How do string pointers work in Arduino?

To the best of my understanding, when I declare String s = "This is a string."; what happens is that space is allocated on the stack for a pointer which points to some String object which internally ...
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0answers
154 views

Overwrite image buffer (inside Adafruit SSD1306)

I'd like to add a method that replaces the entire image buffer into the Adafruit_SSD1306 library. I haven't worked with dynamic memory handling for ages and I'm not sure how to just simply overwrite ...
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1answer
518 views

Selecting different arrays using a list of pointers

I have different arrays of different sizes, and a list of pointers to the addresses of each array. How do I select each array using the list of pointers, and access it's elements. On Teensy 3.2 board. ...
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1answer
4k views

Call by reference

I am trying to learn 'call by reference'. I want to call a function fcn1 from the main loop and pass a reference of the local variable var to the function fcn1. Next step is to call a second function ...
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1answer
63 views

Error with pointer in array

I am currently learning pointers. I am following a book (Says Teach Yourself "Arduino Programming") in which there is an exemple about pointer and array. void setup() { // put your setup code here, ...
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3answers
255 views

How do I create global pointers with low memory overhead?

Problem I have a few large objects in my code that need global visibility, but creating them seems to eat up memory significantly faster than simple math would dictate, and furthermore, using them ...
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1answer
521 views

How do I properly convert a pointer (uint8_t* or void*) to a “normal” integer?

I'm writing a program for arduino that needs dynamic memory allocation frequently, but as I don't want the memory to get fragmented, I'm also writing a "memory handler" for it. This memory handler ...
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2answers
1k views

Receive an array of characters using SIM900 module

I tried to receive an array of characters using SIM900, but I couldn't. I can receive just one character like 'G', but I want to receive a string "abcd". When I used char* to save the SMS, I failed. ...
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2answers
236 views

Send a polymorphic object over serial

I am sending a polymorphic object over serial between two Arduinos. The transmission should be fine, indeed if on the receiver side I static_cast the pointer to the Derived class it works properly. On ...
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3answers
8k views

How to pass a string pointer to a function

I'm working on a project, where I wish to use pointers. I had a very quick overview of using pointers in C in collage, but I don't know how to use them. I want that function uses input String (answer)...
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1answer
877 views

How can I store the received data from nRF24l01+ module in an array (code in description)?

This is my sample RX code for 4 Tx and 1 Rx nRF24l01+ modules. I want to store all the data received from 4 pipes into an array (recArray). #include <SPI.h> #include <nRF24L01.h> #include ...
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2answers
321 views

Initializing pointer to vector of objects inside another object

i want to create a somewhat complex structure of classes in an arduino. The short story is: a Device has Presets, and each Preset has a Patterns. For that i created the following structure (i am only ...
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2answers
7k views

Setting a pointer to NULL in Arduino library - error: ‘NULL’ was not declared in this scope

I am writing my own library for using with my Arduino. In my code, if I set a pointer I have declared to NULL, such as int *ptr=NULL; I get the error error: ‘NULL’ was not declared in this scope I ...
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3answers
607 views

How is a local variable address retrieved/returned inside the CPU of Arduino?

How is the address of a local variable retrieved in Arduino's ATMEGA328 micro-controller? Lets say somewhere inside the main we have lines as: int x = 5; //a variable declared and value of 5 stored ...
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1answer
67 views

Keep References Between Objects

I'm trying to recreate a small tween engine so I can interpolate values, leds hue, saturation and brightness in a easy way. I'm having trouble to reference the value to interpolate into my tween ...
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1answer
6k views

Using pointers with Arduino

I am learning about pointers. I was wondering how the memory address is defined in programming. I get different outputs depending on the format I choose for memory address. So I was wondering if it ...
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1answer
63 views

Pass custom element of an array from an inherited class to main sketch

I'm building a base class that creates color patterns using FastLed's CRGB structure. I use the base class as inheritance for another more specific class that modifies a vector of colors (Pixels[]) ...
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2answers
152 views

Problem with wrapping Adafruit Motor Controller function calls in a class

I'm working on an Arduino robot and I ran into a problem when reorganizing my code. I have an Adafruit Motor Shield v2.3 connected to an Arduino Uno. My robot can be controlled using a bluetooth ...
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2answers
220 views

Pros and Cons of using a non-pointer class object

In this example I have an one object which uses a pointer and one object which does not. class MyClass { public: void myMethod() { // do nothing } }; MyClass* mc1; MyClass mc2; void ...
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3answers
5k views

Storing an array of function pointers

I have some Arduino code that looks like: char packet = ser.read(); switch(packet){ case 'a': someobj.somefunc(); break; case 'b': otherobj.otherfunc(); ...
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1answer
4k views

Remove certain characters from char*

I've got an array of char* with serial data that I'm trying to remove ':' from. I have tried to iterate through the char*, find and remove any colons but it just comes out as garbage. char* espData[...
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2answers
8k views

User callback functions

I want to write a class that allows the user to attach his own function to a member function that listens for messages coming from a wireless module, so that the user's function can be called ...