QDataStream reading to C++ vectors

[pdoria]

Hi,

I have this vector defined:

vector<char> payload;

vector<char> payload;

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and re-sized it to the appropriate size with:

payload.resize(size_packet_data+2);

payload.resize(size_packet_data+2);

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and some QDataStream object like 'mybytes'...

and, as expected I can't do

mybytes >> payload.

mybytes >> payload.

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So, quick question is:
What the best way to read (len) bytes from a QDataStream to a vector?

TIA,
Pedro.

[mcosta]

You can write code like

...
char ch;
for (int i = 0; i < size_packet_data; ++i)
{
    mybytes >> ch;
    payload.push_back(ch);
}
...

...
char ch;
for (int i = 0; i < size_packet_data; ++i)
{
    mybytes >> ch;
    payload.push_back(ch);
}
...

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[pdoria]

Thank you mcosta!

First thing:

It'd only compile if :

mybytes >> (char *&) ch;

mybytes >> (char *&) ch;

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Secondly I'm wondering if there's a more optimized way to do it beyond a for...next loop

TY,
Pedro

[wysota]

and, as expected I can't do

mybytes >> payload.

mybytes >> payload.

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This semantics means "read a vector of items from the stream"

The stream contains something else, I presume, so this will obviously fail.

So, quick question is:
What the best way to read (len) bytes from a QDataStream to a vector?

Having a vector of chars is... well... strange. What you want is QByteArray. Then if you write a byte array to the stream at one end, you can read it on the other:

QByteArray array;
stream >> array;

QByteArray array;
stream >> array;

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Also note QDataStream is not a general purpose binary stream but a (de)serialization mechanism. So if you didn't write a byte array at one end, you can't read it on the other. For that you can use readRawData() or simply QFile API.

[pdoria]

Thank you wysota! (as always to the rescue! )

Let me expose my code:

the structure:

//! \brief Fleet Management Protocol
//! \note All packets related to the fleet management protocol use packet ID 161.
typedef struct {
	quint8 DLE;				// =16;
	quint8 packet_id;			// =161
	quint8 size_packet_data;		// size of fleet_management_payload + 2
	quint16 fleet_management_packet_id;	// see #defines below
	vector<char> fleet_management_payload;	// 0 to 253 bytes
	quint8 checksum;			// compute this BEFORE sending the packet!
	quint8 DLE_end;				// =16
	quint8 ETX;				// =3
} fleet_management_packet_data_type;

//! \brief Fleet Management Protocol
//! \note All packets related to the fleet management protocol use packet ID 161.
typedef struct {
	quint8 DLE;				// =16;
	quint8 packet_id;			// =161
	quint8 size_packet_data;		// size of fleet_management_payload + 2
	quint16 fleet_management_packet_id;	// see #defines below
	vector<char> fleet_management_payload;	// 0 to 253 bytes
	quint8 checksum;			// compute this BEFORE sending the packet!
	quint8 DLE_end;				// =16
	quint8 ETX;				// =3
} fleet_management_packet_data_type;

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the function (so far):

//! \brief Process Fleet Management packets
//! \param records QDataStream raw data
//! \note First two bytes of the packet have already been read by TeltonikaUnit::parseFM4GarminRecs
void processFleetManagement ( QDataStream & records ) {
	fleet_management_packet_data_type packet;
	bool debug = true;
 
	records >> packet.size_packet_data;
	records >> packet.fleet_management_packet_id;
	packet.fleet_management_payload.resize(packet.size_packet_data+2);
 
	// get the payload in a byte at a time...
	char ch;
	for (int i = 0; i < packet.size_packet_data; ++i)
	{
		records >> (char*&) ch;
		packet.fleet_management_payload.push_back(ch);
	}
	records >> packet.checksum;
	records >> packet.DLE_end;
	records >> packet.ETX;
 
}

//! \brief Process Fleet Management packets
//! \param records QDataStream raw data
//! \note First two bytes of the packet have already been read by TeltonikaUnit::parseFM4GarminRecs
void processFleetManagement ( QDataStream & records ) {
	fleet_management_packet_data_type packet;
	bool debug = true;

	records >> packet.size_packet_data;
	records >> packet.fleet_management_packet_id;
	packet.fleet_management_payload.resize(packet.size_packet_data+2);

	// get the payload in a byte at a time...
	char ch;
	for (int i = 0; i < packet.size_packet_data; ++i)
	{
		records >> (char*&) ch;
		packet.fleet_management_payload.push_back(ch);
	}
	records >> packet.checksum;
	records >> packet.DLE_end;
	records >> packet.ETX;

}

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So, as you can see, I'm trying to read packet.size_packet_data bytes from the data stream.
Your suggestion for using a QByteArray is perfectly valid but I'd like to stick with a vector, hence the question in the first place...

TIA,
Pedro.

[wysota]

How was the data written to the device the DataStream operates on?

[mcosta]

You can use

mybytes >> (qint8) ch;

mybytes >> (qint8) ch;

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