struct redefinition problem

Stromberg

Warum geht dass nicht, ich wollte einen Header speziellen Header einführen für Datentypen die ich selbst erfunden habe:

networking_data_types.hpp

#include <string>

struct datum
{
    unsigned long year;
    unsigned long month;
    unsigned long day;
};

struct finance
{
    std::string money_re;
    unsigned long money_amount;
    datum money_date;
};

Und dann hab ich halt überall "networking_data_types.hpp" inkludiert wo ich die Datentypen in meinem code verwenden wollte.
Doch kommt nur imemr n blöder Error:

Project : Console application
Compiler : GNU GCC Compiler (called directly)
Directory : H:\C++ Projekte\Finanzplaner CB\
--------------------------------------------------------------------------------
Switching to target: default
Compiling: main.cpp
In file included from outgo.hpp:4,
from main.cpp:2:
networking_data_types.hpp:4: error: redefinition of struct datum' networking\_data\_types.hpp:4: error: previous definition ofstruct datum'
networking_data_types.hpp:11: error: redefinition of struct finance' networking\_data\_types.hpp:11: error: previous definition ofstruct finance'
Process terminated with status 1 (0 minutes, 0 seconds)

MfG
Stromberg

camper

include guards

#ifndef _NETWORKING_DATA_TYPES_H_ 
#define _NETWORKING_DATA_TYPES_H_ 

#include <string>
struct datum
{
    unsigned long year;
    unsigned long month;
    unsigned long day;
};

struct finance
{
    std::string money_re;
    unsigned long money_amount;
    datum money_date;
};
#endif // _NETWORKING_DATA_TYPES_H_