title: error when compiling c++ code with g++
body: <p>i get error of this type: <br>
  "in function ... multiple definition of ..." <br>
  "... first defined here" <br>
  "warning: size of symbol ... changed from  to  in " <br></p>
  
  <p>*the code is compiled with the flags: -ansi -Wall -pedantic-errors -Werror <br>
  *STL is used <br></p>
  
  <p>is there any explanation for that?
  <br>
  thank you in advance</p>