Questions tagged [pointer]
A variable in C/C++ which stores the type and location of data in memory.
95
questions
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Program crashes when calling external library code via function pointer
I've written a user library for the Pi Pico that uses the TaskScheduler library to abstract timing away from the user. The user provides a function in their sketch which the library calls periodically ...
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2
votes
1
answer
82
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How to pass Encoder object to constructor of a different class
I am trying to create a class (Arm) that controls an arm. The arms have 2 motors, each with an encoder, so I pass 4 integers for the pins and I am trying to pass 2 pointers (one for each encoder ...
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2
answers
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Difference between (*(volatile unsigned int *) and (volatile unsigned int)?
I have been watching tutorials on STM32 bare metal programming. I couldn't understand the purpose of the below code
#define RCC_AHB1EN_R (*(volatile unsigned int *)(RCC_BASE + AHB1EN_R_OFFSET))
and ...
0
votes
4
answers
420
views
How to send multiple bytes with Wire without copying
When I need to send multiple bytes via Wire, for example a long int, I cast it to a byte array and specify a length
long int i;
Wire.write((byte*)&i, 4);
But if I want to send bytes from more ...
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-1
votes
1
answer
536
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Cannot read values stored in bool* pointer [closed]
I'm trying to read values stored in a bool* pointer from a modbus coil call.
I'm using modbus-esp8266 library. it's all ok with Input Registers and Holding Registers but i cannot read the result of a ...
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0
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1
answer
82
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Failure using references variables in classes [closed]
Theoretical Q
I'm having some trouble when using a referenced variable in a class.
Class A have an int a=0. Class B has an instance of Class A, and referencing int &a=A.a, and in the same manner ...
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2
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1k
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Why I cant get sizeof a pointer Array
well I am trying to get array size to convert hex value to int value. but if I try to get size of array it returns every time 2. Actually .I dont understand. how to get array size, can you help me?
...
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2
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Passing a two dimensional array to a function
I'm working on an led matrix project where I'm running a series of patterns made of bitmap frames.
Here's an example: https://vimeo.com/564184465
Right now I'm using a series of method calls named per ...
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1
vote
1
answer
546
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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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0
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1
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483
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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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1
answer
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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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0
votes
1
answer
191
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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 ...
- 103
0
votes
3
answers
908
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,...
- 283
2
votes
1
answer
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Converting c string to integer to unsigned char
I'm grappling 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 an LED ...
- 357
2
votes
2
answers
4k
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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 ...
- 357
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4
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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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1
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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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1
answer
1k
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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 ...
0
votes
1
answer
179
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
votes
1
answer
399
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]) { }
...
0
votes
1
answer
688
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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votes
2
answers
171
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An array of existing arrays
I have a bunch of 3D arrays in the following form:
byte lines[][4][2] {
{ {B00000000, B11110000 },
{B00000000, B11110000 },
{...
- 179
0
votes
1
answer
118
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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 ...
- 13
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1
answer
172
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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/...
- 283
0
votes
1
answer
451
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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 ...
- 103
-1
votes
1
answer
199
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
vote
1
answer
620
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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0
votes
1
answer
167
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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1
vote
4
answers
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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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0
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2k
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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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1
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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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0
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1
answer
186
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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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votes
1
answer
94
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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1
vote
1
answer
160
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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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1
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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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2
votes
2
answers
3k
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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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1
vote
1
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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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3
votes
1
answer
4k
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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votes
1
answer
229
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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1
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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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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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0
votes
0
answers
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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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2
answers
693
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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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1
answer
767
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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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2
votes
1
answer
63
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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votes
1
answer
3k
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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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votes
1
answer
81
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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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1
vote
1
answer
646
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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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1
vote
1
answer
2k
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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 ...
2
votes
0
answers
242
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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