Questions tagged [pointer]

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

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70 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
469 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
877 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
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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
315 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
11k 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
995 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
406 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
10k 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
776 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
69 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
8k 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
66 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
169 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
275 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
5k 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
9k 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 ...
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3answers
261 views

Integer goes garbage after iteration. struct pointer manipulation messed up other variables in memory

I'm writing a library for Charlieplexed LED display (trying to write a common one actually). The library is working quite fine. In my arduino sketch, I'm using an integer to keep track of the LED, ...
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1answer
3k views

Casting a struct member between uint8_t and char, with regard to serial transfer

Im simply trying to pass my payload to another device that has the same architecture and struct. I'm using UART to transfer, and modeling the protocol from EasyTransfer. When I call Serial.print((char*...
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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
963 views

Dereferencing char into a struct

I am sending some data over an NRF24 link, using the RF24Network library. So far I have only sent numbers, now I also want to send a string, so I have set up my payload struct as struct payload_t { ...
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1answer
124 views

Why doesn't my object's method return back to my caller method?

I am creating a miniature computer using an Arduino, and I am creating a full-scale interpreter for it. Everything works, and the code begins to run after calling the runCode method, but once the run ...
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1answer
51 views

Mysterious behavior when using objects

I am writing a project that involves using complementary filters to combine gyroscope and accelerator readings in 3 directions. The relevant code is below. class CompFilter { public: long ...
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2answers
14k views

How can I pass a char array as the parameter to a function?

I am creating a menu for adjusting system variables. The menu is made up of pointers like so: char* options4[] = {"hMin1", "hMax1", "refr1", "fSpeed1"}; I want to pass the selected string as the ...
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1answer
672 views

sending ctrl-z in a struct?

I have a set of buttons wired to an arduino leonardo that are meant to send either single keystrokes to a computer "a, b, c..." etc, or a key sequence like ctrl+z (to perform an undo command.) ...
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1answer
327 views

C++ Pointer Issues - Mangled Data

I am having trouble getting my head around pointers in C++, specifically how they behave when passed around or used within objects. As far as my understanding goes as long as pointers, or more ...
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1answer
307 views

String operators

I have a section of code that I am unsure of what it is doing. static int bufindw = 0; static char buffer[4][96]; static char *strchr_pointer; int result; result = (int)strtod(&buffer[bufindw][...
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2answers
10k views

Pass a member function pointer to a method of a foreign class (EDB Lib)

I'm currently working on my own arduino library and I'm becoming exasperated with the following problem: I want to store data with the extended database library (https://code.google.com/p/arduino-edb/)...
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2answers
209 views

cannot convert error with pointers

I write a code to store patterns for LED blinking, but I got this error: led_basics:39: error: cannot convert 'char (*)[17][2]' to 'char*' in initialization led_basics:39: error: cannot convert '...
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2answers
114 views

Use pointer in calculation results in error

I'm building a project to measure/track flyball dog races. The dogs timings are measured by photoelectric sensors at the start/finish line of the racing lane. I have most of my code working (available ...
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3answers
2k views

ISR executes even though an interrupt is not triggered

I am trying to implement a function queue scheduling system. INT1 is connected to a button and int1task causes an LED to flash. typedef void (*funcptr)(void); TPrioQueue *queue = NULL; void int1ISR()...
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1answer
2k views

Wrong Mouse.move() output in Arduino Leonardo

I'm using my Arduino Leonardo as a Mouse but I'm experimenting a strange behaviour. I put my mouse at (-1, -1) (absolute) coordinates and then I execute this code: Move.move(com[curr_cmd_id].x, com[...
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3answers
1k views

Is it bad coding practice to design a buffer using pointers?

I coded a ring buffer for my Arduino to buffer data from either the SPI or TWI ports. In the .h file I used a pointer for the buffer: typedef uint8_t *ring_buffer_t; typedef uint8_t ring_count_t; ...
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2answers
986 views

Are function pointer assignments atomic in Arduino?

The following snippets are from TimerOne library source code: // TimerOne.h: void (*isrCallback)(); // TimerOne.cpp: ISR(TIMER1_OVF_vect) // interrupt service routine that wraps a user defined ...
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1answer
7k views

How to use String.substring?

I have the following code in which requestLine is always empty and I can't figure out why. request contains a raw HTTP request, and I want to get the first line of the request which contains the ...
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2answers
9k views

Why can I not use pointers instead of array with PROGMEM?

I'm currently changing some libraries to use flash instead of RAM for string storage so that I do not run out of SRAM on a project. Some strings in the library are declared in this manner: const ...

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