Invalid use of incomplete type / log() error

[maad]

Hello everyone!

I searched the web for awhile, but I cant find a solution for my problem. (especially: http://www.cplusplus.com/forum/articles/10627/ was very helpful)All I found was, that this error has something to do with the declaration or the #include of my function, but have a look at my code (I tried to focus, hopefully I don't forget anything important ;-) ):

//myClass.h
namespace program{
  class progEvent;
  
  class myClass
  {
  public:
  int doStuff(program::progEvent &progevent);
  //...//
  }
}

//myClass.cpp
#include "prog_event.h"
#include "myClass.h"
#include <cmath>

int prgram::myClass::doStuff(program::progEvent &progevent)
{
  int size = progevent.vectior1.size(); //Got the "Invalid use of incomplete type" here
  float logSize = 0;
  logSize = log(static_cast<float>(size)); //Got "'log' cannot be used as a function" here
  //..//
  //Do more stuff//
}

Maybe this is a fundamental problem (I'm not a cpp expert), but I used the function progEvent in the entire program and it works well apart from this code here... Did I overlook one thing? Please help me, I'm running out of ideas! Thanks!