Compiler error with std::shared_ptr array initialization

Projects Programming
1

I found some (to me) unexpected behavior when initializing arrays with smart pointers. This minimal example compiles without issue:

#include <memory>

void setup() 
{
  std::shared_ptr<char[]> var(new char[10]);
}

void loop() 
{
  ;
}

Replacing std::unique_ptr<char[]> with std::shared_ptr<char[]> gives a compiler error

cannot convert 'char*' to 'char (*)[]' in initialization

Why the difference?

Side question: Is a custom deleter for arrays necessary in the Arduino IDE (pre- C++17)?

Any insights are appreciated!

2

This section looks like it might be applicable:
std::shared_ptr<T>::shared_ptr - cppreference.com.

3

That seems to work when compiled for a Teensy 3.2:

#include "Arduino.h"
#include <memory>

class FOO {
public:
	FOO() : instance(instanceCount++) {
		Serial.printf("Constructing Instance %d\n", instance);
	}

	~FOO() {
		Serial.printf("Destructing Instance %d\n", instance);
	}
private:
	uint8_t instance;
	static uint8_t instanceCount;
};

uint8_t FOO::instanceCount = 0;

void setup() {
	delay(1000);
	Serial.printf("Creating\n\n");
	std::unique_ptr<FOO[]> arr(new FOO[10]);
	Serial.printf("\nMoving\n");
	std::shared_ptr<FOO> var(std::move(arr));
	auto ptr = var.get();
	Serial.printf("\nPointer = 0x%08X\n", uint32_t(ptr));
	Serial.printf("\nReleasing\n\n");
	var.reset();
	Serial.printf("\nReleased\n");
	ptr = var.get();
	Serial.printf("\nPointer = 0x%08X\n", uint32_t(ptr));
}

void loop() {
}

Result:

Creating

Constructing Instance 0
Constructing Instance 1
Constructing Instance 2
Constructing Instance 3
Constructing Instance 4
Constructing Instance 5
Constructing Instance 6
Constructing Instance 7
Constructing Instance 8
Constructing Instance 9

Moving

Pointer = 0x1FFF9328

Releasing

Destructing Instance 9
Destructing Instance 8
Destructing Instance 7
Destructing Instance 6
Destructing Instance 5
Destructing Instance 4
Destructing Instance 3
Destructing Instance 2
Destructing Instance 1
Destructing Instance 0

Released

Pointer = 0x00000000
4

Thanks for the anwser! I also tried to compile this code

#include <memory>
#include <stdio.h>


int main()
{
    auto var = std::shared_ptr<int[]>(new int[10]);
    printf("Test");
    
    return 0;
}

on onlinegdb.com with C++14 and C++17 - compiles without issue.
The error occured in the Arduino IDE 1.8.13 with the ESP32 Dev Module board - perhaps a bug there?