error C2039 string is not a member of std header file problem

Question

I am having problems with a class I am writing  I have split the class into a  h file that defines the class and an  cpp file that implements the class   I receive this error in Visual Studio 2010 Express   error C2039   string    is not a member of  std   This is the header FMAT h  class string   class FMAT   public      FMAT           FMAT          int session                   private      int manualSession            int autoSession               int     mode             std  string instructionFile            This is the implementation file FMAT cpp   include  lt iostream gt   include  lt string gt   include  FMAT h   FMAT  FMAT         std  cout  lt  lt   manually  1  or instruction file  2  n n       std  cin  gt  gt  mode      if mode    2           std  cout  lt  lt   Enter full path name of instruction file n n           std  cin  gt  gt  instructionFile            int FMAT  session         if mode  1           manualSession         else if mode    2           autoSession               return 1     int FMAT  manualSession          more code     return 0      this is the main file that uses this class   include  FMAT h   int main void        FMAT fmat         create instance of FMAT class      fmat session          this will branch to auto session or manual session      My inability to fix this error is probably a result of me not understanding how to properly structure a class into separate files  Feel free to provide some tips on how to handle multiple files in a c   program

User · Answer

Your FMAT h requires a definition of std  string in order to complete the definition of class FMAT  In FMAT cpp  you ve done this by  include  lt string gt  before  include  FMAT h   You haven t done that in your main file   Your attempt to forward declare string was incorrect on two levels  First you need a fully qualified name  std  string  Second this works only for pointers and references  not for variables of the declared type  a forward declaration doesn t give the compiler enough information about what to embed in the class you re defining

User · Answer

Take care not to include    include  lt string h gt     but only    include  lt string gt    It took me 1 hour to find this in my code   Hope this can help

User · Answer

You need to have   include  lt string gt    in the header file too The forward declaration on it s own doesn t do enough   Also strongly consider header guards for your header files to avoid possible future problems as your project grows  So at the top do something like    ifndef THE FILE NAME H  define THE FILE NAME H     header goes in here      endif   This will prevent the header file from being  included multiple times  if you don t have such a guard then you can have issues with multiple declarations

[c++] error C2039: 'string' : is not a member of 'std', header file problem

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