Databases
StackOverflow2013
Postsdbo
POFunction pointer to a non-static member function when the class type is unknown?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POFunction pointer to a non-static member function when the class type is unknown?
    primarykey
    data
    text
    <p>I'm working on a game project that features scratch-built controls rendered into an opengl context; things like buttons, scrollbars, listboxes, etc. Many of these controls are nested; for example, my listbox has a scrollbar, a scrollbar has 3 buttons, etc. </p> <p>When a scrollbar changes value, I'd like it to call 'some' function (typically in it's parent object) that responds to the change. For example, if the listbox has a slider, it should instantiate the slider, then tell the new slider that it should call the listboxes 'onScroll(float)' function. All of the controls share a common base class, so I could have a 'base* parent' parent pointer, then do 'parent->onScroll(val)'. The problem though is what happens when the parent doesn't inheirit from base; there'd be no virtual onScroll() to follow through, so the top-level parent would have to periodically check to see if any of the child controls had changed value. This would also clutter up other controls, since they may not even have children, or may require different event types like when a list entry object is selected, etc.</p> <p>A better solution would be to have the child object maintain a generic function pointer (like a callback), which can be set by the parent, and called by the child as necessary. Something like this:</p> <pre><code>typedef (*ptFuncF)(float); class glBase { public: //position,isVisible,virtual mouseDown(x,y),etc }; class glDerivedChild : public glBase { public: glDerivedChild(); ~glDerivedChild(); void changeValue(float fIn) { Value = fIn; //ignore these forward declaration errors (*callBack)(fIn); } void setCallBack(ptFuncF pIn) {callBack = pIn;} ptFuncF callBack; float Value; }; class glDerivedParent : public glBase { public: glDerivedParent() { child = new glDerivedChild(); child-&gt;setCallBack(&amp;onScroll); } ~glDerivedParent() {delete child;} void onScroll(float fIn) { //do something } glDerivedChild* child; }; class someFoo { public: someFoo() { child-&gt;setCallBack(&amp;setValue); } void setValue(float fIn) { //do something else } glDerivedChild child; }; </code></pre> <p>I'm kinda new to function pointers, so I know I'm (obviously) doing many things wrong. I suspect it might involve something like "typedef (glBase::*ptFuncF)(float);" with the 'onScroll(f)' being an overridden virtual function, perhaps with a generic name like 'virtual void childCallBack(float)'. I'd prefer to keep the solution as close to vanilla as possible, so I want to avoid external libraries like boost. I've been scratching my head over this one for the better part of 8 hours, and I'm hoping someone can help. Thanks!</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USGhost2
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POFunction pointer to a non-static member function when the class type is unknown?
      1. This table or related slice is empty.
      1. VTDownMod
    1. CODid you try `typedef (glBase::*ptFuncF)(float);`? What happened?
      singulars
      1. POFunction pointer to a non-static member function when the class type is unknown?
      1. USShahbaz
    2. COThe problem is that that only seems to work with static member functions, and I need it to call a function specific to a class instance.
      singulars
      1. POFunction pointer to a non-static member function when the class type is unknown?
      1. USGhost2
    3. COThat's not true. Let me post as an answer.
      singulars
      1. POFunction pointer to a non-static member function when the class type is unknown?
      1. USShahbaz
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload