Short werte aus Array von Bytes lassen sich nicht ablesen oder kasten

[o4kareg]

Wie soll ich in C++ kasten , so dass ich in den Array von Bytes die 2 -Bytes
Werte (short) ablesen könnte ?

beim

reinterpret_cast<uint16_t *>(...)

kommt ein Fehlermeldung raus :
error: reinterpret_cast from type ‘const uint8_t* {aka const unsigned char*}’ to type ‘uint16_t* {aka short unsigned int*}’ casts away qualifiers

[IrgendeinName]

o4kareg schrieb:

Wie soll ich in C++ kasten , so dass ich in den Array von Bytes die 2 -Bytes
Werte (short) ablesen könnte ?

beim

reinterpret_cast<uint16_t *>(...)

kommt ein Fehlermeldung raus :
error: reinterpret_cast from type ‘const uint8_t* {aka const unsigned char*}’ to type ‘uint16_t* {aka short unsigned int*}’ casts away qualifiers

Öhm.. du darfst in C++ const nicht wegcasten. Außer du verwendest const_cast

EDIT: Und ich glaube nicht das das casten das machst was du dir vorstellst.

[o4kareg]

Danke, es war voll unklar das das ding wegen Const meckert.

Eine ziemlich korrekte Lösung wäre dann:

const uint16_t * lvl2Num = reinterpret_cast<const uint16_t *> (paket +toLook);

Omg, es funktioniert, aber dabei werden die bytes umgetausht
Nee, c++ macht doch fertig!

[logoffters]

Du willst also ein Short in 2 Byte splitten:
Ungefähr so?

#include <iostream>

unsigned char extract(unsigned short in, unsigned short lowerBound, unsigned short upperBound)
{
	if (upperBound > 8)
	{
		lowerBound -= 8;
		upperBound -= 8;
		in /= 128;
	}

	unsigned char result = 0;
	for (unsigned char i = 1 << (upperBound - 1); i >= lowerBound; i >>= 1)
	{
		if (in & i)
			result += i;
	}
	return result;
}

//Testcode
int main()
{
	unsigned short tmp = 4244;
	unsigned char ch1 = extract(tmp,1,8);
	unsigned char ch2 = extract(tmp,9,16);
	std::cout << static_cast<int>(ch1) << '\n';
	std::cout << static_cast<int>(ch2) << '\n';
}

[Korrigierer]

logoffters schrieb:

Du willst also ein Short in 2 Byte splitten:
Ungefähr so?

#include <iostream>

unsigned char extract(unsigned short in, unsigned short lowerBound, unsigned short upperBound)
{
	if (upperBound > 8)
	{
		lowerBound -= 8;
		upperBound -= 8;
		in /= 128;
	}

	unsigned char result = 0;
	for (unsigned char i = 1 << (upperBound - 1); i >= lowerBound; i >>= 1)
	{
		if (in & i)
			result += i;
	}
	return result;
}

//Testcode
int main()
{
	unsigned short tmp = 4244;
	unsigned char ch1 = extract(tmp,1,8);
	unsigned char ch2 = extract(tmp,9,16);
	std::cout << static_cast<int>(ch1) << '\n';
	std::cout << static_cast<int>(ch2) << '\n';
}

#include <iostream>

unsigned char extract(unsigned short in, unsigned short lowerBound, unsigned short upperBound)
{
	unsigned char result = 0;

	if (upperBound > 8)
		result = in / 256;

	else
	{

	for (unsigned char i = 1 << (upperBound - 1); i >= lowerBound; i >>= 1)
	{
		if (in & i)
			result += i;
	}
	return result;
	}
}

int main()
{
	unsigned short tmp = 25524;
	unsigned char ch1 = extract(tmp,1,8);
	unsigned char ch2 = extract(tmp,9,16);
	std::cout << static_cast<int>(ch1) << '\n';
	std::cout << static_cast<int>(ch2) << '\n';

Wohl eher so.

[Korrigierer]

unsigned char extract(unsigned short in, unsigned short lowerBound, unsigned short upperBound)
{
	unsigned char result = 0;

	if (upperBound > 8)
		result = in / 256;

	else
	{

		for (unsigned char i = 1 << (upperBound - 1); i >= lowerBound; i >>= 1)
		{
			if (in & i)
				result += i;
		}
	}
	return result;

}

MIST! Fehler gemacht bei Klammern.