qmake "The *= operator"

 

今天浏览了下Qtwenkit的测试例子（./src/testlib/testlib.pro），发现其中的pro中有：

DEFINES *= QT_NO_CAST_TO_ASCII \
    QT_NO_CAST_FROM_ASCII \
    QTESTLIB_MAKEDLL \
    QT_NO_DATASTREAM
 
 对 *= 赋值的意思有点模糊了，应该是如果没有赋值过才执行赋值的意思。 经查看文档，确认了就是这个意思：
 
The *= operator adds a value to the list of values in a variable, but only if it is not already present. This prevents values from being included many times in a variable. For example:
  下面例子：如果还没有定义QT_DLL，那么就定义它：
 DEFINES *= QT_DLL
In the above line, QT_DLL will only be added to the list of pre-processor defines if it is not already defined. Note that the unique() function can also be used to ensure that a variables only contains one instance of each value.

The ~= operator replaces any values that match a regular expression with the specified value:

 DEFINES ~= s/QT_[DT].+/QT
In the above line, any values in the list that start with QT_D or QT_T are replaced with QT.