Questions tagged [pointer]

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

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3answers
145 views

Run multiple function with different argument/return structure by one function pointer

Edit: I tried a simple code in Arduino IDE which should've done in the first place instead in doing it in a desktop compiler. Because the results are different by experiment. In the desktop C compiler,...
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1answer
887 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
41 views

esp32 crashes when trying to dereference a pointer value

I have a websocket listener that is giving me a std::string of my message payload (I want the bytes) and I wrote a function that pulls each of the bytes out and puts them into 32 bit integer variables,...
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1answer
65 views

converting an unsigned integer into a const char pointer

I know this is simple basic C stuff, but I can't quite figure it out or find a solution when searching and reading. I have a method I want to call from a library that wants a const char pointer ...
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5answers
4k views

Why is it considered bad practice to use the 'new' keyword in Arduino?

I previously asked this question: Is it required to delete variables before going to sleep? On that question, @Delta_G posted this comment: ... Really on a microcontroller I would create the object ...
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1answer
80 views

Can you create an array for functions? [closed]

Let's say I want to create 10 functions, named Function1, Function2 until 10. Each function is used if a certain variable is equal to its number. Rather than using individual functions, I was ...
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1answer
30 views

Accessing funcition in object via `->` is crashing (resetting) Arduino

I have several classes that call each other running on an Arduino Mega. I am using the ArduinoSTL library to get the std library, most notably the std::vector. The core problem is as follows: my ...
2
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1answer
80 views

Converting c string to integer to unsigned char

I'm Trying to grapple with types between two different libraries. The gist is that I'm using the ArduinoWebsockets library to receive information coming from my api that I then want to render out to ...
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2answers
171 views

Issues converting an uint32_t into a char*

I'm using a capacitive touch sensor that as 12 touch points and stores it's state data as a binary number. I want to take that state, add a bit of data onto the front, and then send it up to a server ...
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2answers
48 views

An array of existing arrays

I have a bunch of 3D arrays in the following form: byte lines[][4][2] { { {B00000000, B11110000 }, {B00000000, B11110000 }, {...
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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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1answer
43 views

How to specify a timer's name depending on the chip it will be compiled to?

I need to enable a timer interrupt for a chip, and in the mean time, I am testing the code on Arduino Nano rather than (feed the chip, test the chip)++. So as part of the code I have to TIMSK0 |= (1 &...
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1answer
346 views

Setting an array pointer to null on declaration

How can I set an array pointer to null? I have a pointer to a 3 int array that I am trying to set to null. int (*EXCLUSIVE_COLOR)[3]; Per this link I was trying to set it to null upon ...
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1answer
62 views

Assigning an empty array row to reference [duplicate]

int colors[][3] = { { 255, 0, 0 }, { 0, 255, 0 }, { 0, 0, 255 }, { 253, 7, 210 } }; int (*EXCLUSIVE_COLOR)[3]; I have a two-dimensional array to store some color values. I have a 2nd ...
0
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1answer
127 views

Error taking address of temporary array when passing compound literal array

I have an Arduino sketch that passes an array into a method as a compound literal, but for some reason I keep getting the following error: void setup() { } void printConcatLine(char chunks[][20]) { } ...
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1answer
52 views

Swap two arrays (using pointers, not copy)

I've got two arrays, defined as: uint8_t array1[10]; uint8_t array2[10]; I'd like to swap the arrays (actually the pointers to each array) using code like this: uint8_t *tmp = array1; array1 = ...
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1answer
49 views

Boolean function call with character pointer input - dont understand how to get updated pointer value

Thank you for everyone's help in trying to find a solution. This library I'm working with was prewritten and is one of the most buggy hardware libraries I've had the misfortune to use. I have now ...
0
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1answer
55 views

Function pointers that call one function

I'm reading a library file timer.h for STM core library that I just installed in Arduino hardware folder. Of course, there has to be a lot of questions for me as a beginner about many approaches/...
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1answer
154 views

Passing a NeoPixel object reference to a custom library

I'm new to Arduino programming and haven't programmed in C++ in the past. I'm trying to create a custom library to cycle a rainbow on my NeoPixel LED strip. I want to pass a reference or pointer or ...
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1answer
81 views

Multiple Serial Ports Stream Switch

I am trying to define multiple serial ports (multiple BMS management boards) and select via a global variable the port which one is active, this is the sketch I am trying to modify. https://github....
1
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1answer
29 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(); ...
5
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3answers
4k views

Works with gcc, not with Arduino. error: taking address of temporary array

I need to hard code 8 byte addresses into char arrays of length 8. This must be done many places in my code (in function scope), so I have tried to come up with a one-liner. The following works ...
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1answer
51 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
545 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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0answers
719 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
137 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
65 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 ...
3
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1answer
55 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
68 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
40 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 ...
2
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0answers
132 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: ...
2
votes
2answers
658 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 ...
2
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1answer
1k 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
63 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) { ...
0
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1answer
626 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
120 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
1k 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
101 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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0answers
75 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 ...
1
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2answers
398 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 ...
1
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1answer
414 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 ...
1
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1answer
56 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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1answer
65 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
272 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 ...
1
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1answer
942 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 ...
0
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2answers
617 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
74 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
423 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 ...
1
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1answer
1k 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 ...
0
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0answers
195 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 ...