Question

I am using QRegExp and tries to find whether a QString is containing some pattern. There is no compiling error, but no match is identified at runtime where identification should normally happen. I tested the regexp in Python shell and match occurs with Python. i checked upon Qt doc that syntax is the same for the ergexp I am using. Here is code sample

 bool Thing::isConstraint(const QString &cstr_)
 {



QRegExp lB1("^(\d+\.?\d*|\d*\.\d+)<=PARAM(\d+)$");
QRegExp lB2("^PARAM(\d+)>=(\d+\.?\d*|\d*\.\d+)$");
QRegExp lB3("^PARAM(\d+)>(\d+\.?\d*|\d*\.\d+)$");
QRegExp lB4("^(\d+\.?\d*|\d*\.\d+)<PARAM(\d+)$");

QRegExp uB5("^(\d+\.?\d*|\d*\.\d+)>=PARAM(\d+)$");
QRegExp uB6("^(\d+\.?\d*|\d*\.\d+)>PARAM(\d+)$");
QRegExp uB7("^PARAM(\d+)<=(\d+\.?\d*|\d*\.\d+)$");
QRegExp uB8("^PARAM(\d+)<(\d+\.?\d*|\d*\.\d+)$");


QRegExp luB9("^(\d+\.?\d*|\d*\.\d+)>=PARAM(\d+)>=(\d+\.?\d*|\d*\.\d+)$");
QRegExp luB10("^(\d+\.?\d*|\d*\.\d+)>PARAM(\d+)>=(\d+\.?\d*|\d*\.\d+)$");
QRegExp luB11("^(\d+\.?\d*|\d*\.\d+)>=PARAM(\d+)>(\d+\.?\d*|\d*\.\d+)$");
QRegExp luB12("^(\d+\.?\d*|\d*\.\d+)>PARAM(\d+)>(\\d+\.?\d*|\d*\.\d+)$");
QRegExp luB13("^(\d+\.?\d*|\d*\.\d+)<=PARAM(\d+)<=(\d+\.?\d*|\d*\.\d+)$");
QRegExp luB14("^(\d+\.?\d*|\d*\.\d+)<=PARAM(\d+)<(\d+\.?\d*|\d*\.\d+)$");
QRegExp luB15("^(\d+\.?\d*|\d*\.\d+)<PARAM(\d+)<=(\d+\.?\d*|\d*\.\d+)$");
QRegExp luB16("^(\d+\.?\d*|\d*\.\d+)<PARAM(\d+)<(\d+\.?\d*|\d*\.\d+)$");

int pos_=0;

if((pos_ = lB1.indexIn(cstr_)) != -1)
{
    m_func->setLowerBound((lB1.cap(2)).toInt(),(lB1.cap(1)).toDouble());
    return true;
}

else if((pos_ = lB2.indexIn(cstr_)) != -1)
{
    m_func->setLowerBound((lB2.cap(1)).toInt(),(lB2.cap(2)).toDouble());
    return true;
}

      /*
         ...
      */
      return false;
   }

This method is called in this other method:

void Thing::setConstraints(QStringList &constraints_)
{
if(!m_func)
return;

 for(int j=0;j<constraints_.size();j++)
{

    if(isConstraint(constraints_.at(j)))
    {
        constraints_.removeAt(j);
    }
}
m_func->setConstraints(constraints_);
 }

In VS2010 Watch, error for lB1.indexIn(cstr_) is: Error: argument list does not match a function .

Second, I would like the isConstraint() method to begin with this check and replace for whitespaces:

     QRegExp wsp ("\s+");
cstr_.replace(wsp,"");

how to proceed avoiding const_cast ??

Thanks and regards.

edit ———
needed to double backslash in C++ – different from Python. Tks!

Answer 1

I think you asked two questions, so I’ll try to answer them:

1) Your regular expressions are most likely not passing because you need to escape your backslashes so that C++ doesn’t mess up your strings. For example:

QRegExp lB1("^(\\d+\\.?\\d*|\\d*\\.\\d+)<=PARAM(\\d+)$");

2) To avoid using const_cast you can either change your function signature to this:

 bool Thing::isConstraint( QString cstr_)

or make a copy of the cstr_ object and operate on the copy instead.

As a side note, you may want to take a look at the QRegExp::exactMatch() function which obviates the need to use ^ and $ at the beginning and end of all of your expressions, and also has a bool return value which would make your if statements a little cleaner.