primitives rotation around x, y, z axis in World Space by slider

Primitives (here cube) are centred in World Space. I want to rotate them by slider as in image below.


So far I’m using this code:

This is rot object definition:

struct rotation
    float x = 180;
    float y = 180;
    float z = 180;

This stuff is executed when user changes slider’s position

void MyFrame::OnSliderChanged(wxScrollEvent &event)
    //cur_sel is currently selected primitive and scene
    case ID_SLIDER0: //slider X
        GLCanvas->rot[GLCanvas->cur_sel].x = event.GetPosition();
    case ID_SLIDER1: //slider Y
        GLCanvas->rot[GLCanvas->cur_sel].y = event.GetPosition();
    case ID_SLIDER2: //slider Z
        GLCanvas->rot[GLCanvas->cur_sel].z = event.GetPosition();

This stuff is executed all time (on frames change):

glRotatef(rot[cur_sel].x,rot[cur_sel].x, 0.0f,  0.0f);
glRotatef(rot[cur_sel].y,0.0f,  rot[cur_sel].y, 0.0f);
glRotatef(rot[cur_sel].z,0.0f,  0.0f, rot[cur_sel].z);

I know it isn’t good approach because sometimes ( when I mix x,y,z positions) rotations aren’t performed properly. For example when I rotate around x axis it looks like it was turned around y axis.

I’m looking for properly approach.