class member functions vs free functions

If the function might be used elsewhere then it's a candidate for outside of the class. If it's only going to be used within the class, then it's a good choice for a class member.

Here is an article that might be of interest.

i read that article and i understand some of it but i still feel like my awnser is not found there. i understand of course the more functions u add/change in a class increase the chance of breaking/rendering the class usesless. But i'm still unsure of how to determine what functions needs to be member functions, and what functions needs to be non member functions.

class Process
{
private:
std::wstring processName;
int processID;
handle processHandle;
public:
Process(const std::wstring processName);
~Process();
isValidProcess(); <--- i was told this should be a nonmember function but i'm unsure why!
};

i feel like if i want this class to be successfull it should have a function in it which can perform error checking so the user can validate whether the process is actually a valid process on the system. What if i release process class that is below which doesn't contain any error checking

class Process
{
private:
std::wstring processName;
int processID;
handle processHandle;
public:
Process(const std::wstring processName);
~Process();
};


my proce

If isValidProcess() is a free function, how can it determine whether the process is valid?

The rule of thumb is to use free functions when you can, and member functions when you must. Member functions should be those that manage invariants or require access to private data.