QUdpSocket相关 （1）
随手试了下C++ GUI Programming with Qt4 UdpSocket中的例子。
void testDialog::sendDatagram()
{
ss1 = lineEdit1->text();
ss2 = lineEdit2->text();
ints = lineEdit3->text().toInt();
QByteArray datagram;
QDataStream out(&datagram,QIODevice::WriteOnly);
out.setVersion(QDataStream::Qt_4_7);
out<<ss1<<ss2<<ints;
udpsocket.writeDatagram(datagram,QHostAddress::LocalHost,6000);
}
函数解释:pendingDatagramSize 当有数据包读入时返回true.resize 为datageam设置大小pendingDatagramSize 返回udosocket第一个数据包的大小
.....................................
connect(&udpsocket,SIGNAL(readyRead()),this,SLOT(recvDatagram()));
udpsocket.bind(QHostAddress::LocalHost,6000);
}
void testDialog::recvDatagram()
{
QByteArray datagram;
do{
datagram.resize(udpsocket.pendingDatagramSize());
udpsocket.readDatagram(datagram.data(),datagram.size());
}while(udpsocket.hasPendingDatagrams());
QDataStream in(&datagram,QIODevice::ReadOnly);
in.setVersion(QDataStream::Qt_4_7);
in>>ss1S>>ss2S>>intsS;
label->setText(ss1S+ss2S+QString::number(intsS));
}
1， resize 把datageam大小设置为pendingDatagramSize()返回udosocket第一个数据包的大小。
2， readDatagram()
qint64 QUdpSocket::readDatagram ( char * data, qint64 maxSize, QHostAddress * address = 0, quint16 * port = 0 )
Receives a datagram no larger than maxSize bytes and stores it in data. The sender's host address and port is stored in *address and *port (unless the pointers are 0).Returns the size of the datagram on success; otherwise returns -1.
接受不超过maxSize大小的数据包，并吧它存储在data中。3， char * QByteArray::data ()
Returns a pointer to the data stored in the byte array. The pointer can be used to access and modify the bytes that compose the array. The data is '\0'-terminated, i.e. the number of bytes in the returned character string is size() + 1 for the '\0' terminator.
返回存储在字节数组中数据的指针。
4， int QByteArray::size () const
Returns the number of bytes in this byte array.
返回一个字节数组的字节元素数量，从零开始。
The last byte in the byte array is at position size() - 1. In addition, QByteArray ensures that the byte at position size() is always '\0', so that you can use the return value of data() and constData() as arguments to functions that expect '\0'-terminated strings.
Example:
QByteArray ba("Hello");
int n = ba.size(); // n == 5
ba.data()[0]; // returns 'H'
ba.data()[4]; // returns 'o'
ba.data()[5]; // returns '\0'
5， bool QUdpSocket::hasPendingDatagrams () const
Returns true if at least one datagram is waiting to be read; otherwise returns false.
返回true，当至少有一个数据报等待读取的情况下。否则返回false.
Returns the size of the first pending UDP datagram. If there is no datagram available, this function returns -1.
C++ GUi with Qt4书中说，在readyRead信号发送前，发送端可能已经接收了部分数据报。但应为书中的例子是气象气球，书中说因为以前的数据都是过去的天气，已经过时了，所以不需要处理了。作者真会选择例子。。。= =#