How to receive properly using QDataStream

azhagan2

Hi , I tried to receive some structure variables from server side through socket by write function, and i tried to receive those in Qt QDatastream , but cant able to receive properly , only first int variable is receiving properly , remaining are not.
this is my struct and code

struct my_struct
{
int a;
char b[100];
char c[100];
int d;
char e[100];
};

QDataStream in(mysocket);
in.setByteOrder(QDataStream::LittleEndian);
my_struct s;
in>>s.a;
const int b_size = sizeof(s.b);
in.readRawData(s.b, b_size);
//s.b[b_size+1] = '\0';
const int c_size = sizeof(s.c);
in.readRawData(s.c, c_size);
s.c[c_size+1] = '\0';

in>>s.d;

const int e_size = sizeof(s.e);
in.readRawData(s.e,e_size);
s.e[e_size+1] = '\0';

QString b(s.b);
QString c(s.c);
QString e(s.e);
ui->plainTextEdit_2->clear();
result = QString("Received Data : \n Msg No. = %1, \n Message = %2, \n Msg dir. = %3, \n Msg Id = %4 \n Msg_end = %5 \n").arg(s.a).arg(b).arg(c).arg(s.d).arg(e);

Axel Spoerl

Using QDataStream for this purpose is very hairy and not recommended.
It works only if the serialization is exactly the same on both sides. It’s not a type safe operation.
Better to use JSON for transmission of structured data.

jsulm

@azhagan2 Does the server also use QDataStream? If now you can't use QDataStream on receiver side.

ChrisW67

@azhagan2 said in How to receive properly using QDataStream. See comments in the code

QDataStream in(mysocket);
in.setByteOrder(QDataStream::LittleEndian);
my_struct s;
in>>s.a;  
// ^^  OK if the writer used the same int size and byte order.
const int b_size = sizeof(s.b);
// ^^ b_size = 100
in.readRawData(s.b, b_size);
// ^^ How many bytes were read?  100, or something else.  Were bytes there to be read?
//s.b[b_size+1] = '\0';
// ^^ set the 101st byte to zero!  Buffer overflow
const int c_size = sizeof(s.c);
// ^^ c_size = 100
in.readRawData(s.c, c_size);
// ^^ How many bytes were read?  
s.c[c_size+1] = '\0';
// ^^ set the 101st byte to zero!  Buffer overflow
in>>s.d;
// ^^ Maybe if you are still in sync with the sent packet.
const int e_size = sizeof(s.e);
in.readRawData(s.e,e_size);
s.e[e_size+1] = '\0';

azhagan2

@jsulm No , server not using QDataStream

Axel Spoerl

@jsulm No , server not using QDataStream

Then QDataStream is definitively not what should be used. It's not type safe as said before.
Which format is the server sending? What's the nature of the connection?

azhagan2

@Axel-Spoer l Iam sending those structures through TCP sockets using send/write function.

JonB

@azhagan2
That in itself doesn't say much. It's more about in what "format" or what "protocol" you are sending data.

In any case QDataStream is not for use here, it's only for if both sides are written in Qt and using it. You should either use "raw" reads/writes, and make sure about things like what the endian ordering is both sides and how you might send, say, a string, or as @Axel-Spoerl says maybe use JSON for more complex but still structured data.

azhagan2

Thanks Everybody , all the replies helped me out :)