错误信息：
undefined reference to`_imp___ZN10QTcpSocketD1Ev'
undefined reference to `_imp___ZN10QTcpSocketC1EP7QObject'
undefined reference to `_imp___ZN10QTcpSocketD1Ev'
undefined reference to `_imp___ZN10QTcpSocketD1Ev'
undefined reference to `_imp___ZN10QTcpSocketD1Ev'
undefined reference to `_imp___ZN10QTcpSocketD1Ev'
undefined reference to `_imp___ZN10QTcpSocketD1Ev'
undefined reference to`_imp___ZN15QAbstractSocket13connectToHostERK7QStringt6QFlagsIN9QIODevice12OpenModeFlagEE'
undefined reference to `_imp___ZN15QAbstractSocket5closeEv'
collect2: ld returned 1 exit status
解决方案：
链接库问题，在工程文件（.pro）文件中
QT += core gui network
加上network选项
