How to fix discards qualifiers [-fpermissive] for cv::SVMParams? - c++

Question

I have a class ConfigFile that has a getter for the SVMParams member:
cv::SVMParams gerSVMParams()
{
return *m_mapConfig["SVMParams"];
}
The code is a little bit more complicated. m_mapConfig is a
std::map<std::string, std::unique_ptr< IConfigItem > >
And IConfigItem is a template class that looks like this for SVMParams:
template<> class ConfigItem< cv::SVMParams > : public IConfigItem
{
private:
cv::SVMParams m_value;
public:
ConfigItem(const cv::SVMParams& valueIn) : m_value(valueIn) {}
operator cv::SVMParams() const
{
return m_value;
}
};
My problem is when I am trying to auto train the SVM classifier:
classifier.train_auto(trainingData, classes, cv::Mat(), cv::Mat(), configFileIn.getSVMParams());
I am getting an error of kind:
error: passing ‘const ConfigFile’ as ‘this’ argument of ‘cv::SVMParams ConfigFile::getSVMParams()’ discards qualifiers [-fpermissive]
Any suggestions of what I am doing wrong? Or is there a small bug because because the train_auto functions has no const in front of the SVMParams parameter. Or is it modifying it?

Answer 1

Make your function const:
cv::SVMParams gerSVMParams() const
// ^^^^^
The error is you are calling a non-const method on a const object, which the compiler rejects as being potentially unsafe. That said, your implementation is inherently non-const too since you might be inserting an object into your map, so just adding the const won't help.
What you probably want to do is:
cv::SVMParams gerSVMParams() const
// ^^^^^
{
auto it = m_mapConfig.find("SVMParams");
if (it != m_mapConfig.end()) {
return *(*it);
}
else {
return {}; // maybe?
}
}

Answer 2

Found the problem: I was calling the function in which I was calling the getSVMParams() with const ConfigFile&; and that was not allowed by the shared_ptr I used in the map.
Thanks all, anyway!