Sending data over socket from C server to qt Client - c++

Question

I am in bit of a problematic situation here:
I have a simple C server (can't use Qt TcpServer, limitations of the embedded board) which sends double data (generated by GPIO ports) over tcpsocket using send(). If I have a simple C client (in my Linux PC) then I am able to get the real time data as is generated with the help of recv(). Here is my server code:
int main (void){
int s,b,l,fd,sa,bytes,on=1;
char buf[BUF_SIZE],fname[255];
struct sockaddr_in channel;
long long sum=0;
double average=0;
int i,j;
int srno=0;
s=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
if(s<0)
{
printf("socket creation failure");
exit(0);
}
setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *)&on,sizeof(on));
memset(&channel,0,sizeof(channel));
channel.sin_family=AF_INET;
channel.sin_addr.s_addr=htonl(INADDR_ANY);
channel.sin_port=htons(SERVER_PORT);
b=bind(s, (struct sockaddr *)&channel,sizeof(channel));
if(b<0)
{
printf("bind error");
exit(0);
}
listen(s,5);
while(1)
{
printf("waiting for request\n");
sa=accept(s,0,0);
if(sa<0)
{
printf("accept failure");
}
for (i=1; i<=56; i++) //for 10 sec >> 56
{
for(j=1;j<=20;j++)
{
//more than 100 lines of code here
}
average=(sum/20)*1.22;
send(sa, &average, sizeof(average), 0);
//int tmp = htonl((uint32_t)average); //tried this also
//send(sa, &tmp, sizeof(tmp), 0);
// int n = write(sa, &average, sizeof(average)) //and tried this also
// if(n<0){
// printf("error");}
printf("%lld \n", average);
srno++;
sum=0;
average=0;
}
}
remove_gpio();
close(s);
return 0;
}
But I am unable to get to display the data in Qt Client, it is driving me crazy. In my QtextEdit I get non-ASCII characters, whatever I try. inside my startRead() I did
...
QByteArray Data = socket->readAll();
ui->textEdit->append(QString(Data));
...
I also tried using other methods bytesavailable() canreadLine(), and also went through other links but was unsuccessful.
Non-ASCII crazy characters is what I get everytime. Sorry not able to give a pic due to low rep.
I need help regarding sending double data through socket and be able to work with the data or atleast display them in a QTextEdit/QPlainTextEdit.
Thanks.

Answer 1

as ciphor said you are trying to display binary directly as text
you'll want to use a datastream to convert
QByteArray Data = socket->readAll();
QDataStream dstream (Data);
double d;
while(!dstream.atEnd())
{
dstream >> d;
ui->textEdit->append(QString::number(d));
}

Answer 2

You need to actually design, specify, and implement a protocol. Otherwise, it's as if your client is speaking Chinese and your server listening for Spanish. Because TCP is a byte-stream protocol, you need to precisely specify how the two programs will interchange data as a stream of bytes. Then design both sides to send a stream of bytes in accord with the specification and receive a stream of bytes in accord with the specification. To help you get started, you should thoroughly study the specifications for existing protocols layered on top of TCP such as IRC, NNTP, SMTP, IMAP, and so on.

Answer 3

The conversion specifier for double is "lf".
The "lld" the code is using is for long long integer.
So use:
printf("%lf\n", average);

Answer 4

You are sending the data in format of double precision binary, but trying to display as a string in your client, that is the reason of non-ASCII.
If you want to send ASCII, you should convert the data into string format before sending it at server side.
char buf[20] = {0};
average=(sum/20)*1.22;
sprintf(buf, "%lld", average);
send(sa, &buf[0], strlen(buf), 0);