Does the order of #include directives and "using" statements matter at the beginning of a C++ header file? -

i cleaning c++ header file , have noticed following:

#if !defined(header_h_) #define header_h_  #include <vector> #include <string>  using namespace std;  #include<stdio.h>  #include "blar/obja/model.h"  namespace blar{   class blar; }  #include <blar/blar.h> #include <blar/objb/othermodel.h>  using namespace blar;  #include <utilities/otherthing.h>   #include <qstringlist.h> 

is bad practice, or of ramifications of each #include/using/namespace related declaration depend on order? since there no code in between, wouldn't think so, i'm not familiar many subtleties...

if headers written doesn't matter. if have inter-dependencies makes great deal of difference.

// header 1 #undef foo #define foo 1  // header 2 #undef foo #define foo 2 

that's silly example, it's easy, if you're not careful, similar conflicts without using preprocessor.