c ++, declare a struct as a global variable

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c ++, declare a struct as a global variable

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C ++, when declaring a struct as a global variable, later I can not access it from an object (class) ... The development environment consists of three files:

the 1st file contains the main pgm, so the variable is defined:

struct  stXXX {
    TIMESTAMP_STRUCT  timestamp; // Horario de generación del registro en tabla VarProceso
    double            contador;  // Cantidad de bolas ingresadas
    float             diametro;  // Diametro de bolas ingresadas
} stXXX;

the 2nd file is a header for the declaration of the class.
the 3rd file contains the code (c ++) of the object that is invoked from the 1st file.

The struct is declared before the main() in the 1st file, if I use it in the main pgm, it does not generate any errors.

The compiler warns me that the "identifier stXXX is undefined" when I use it in the 3rd file.

I manage the project with Microsoft Visual Studio Community 2015

My questions are:

a.- Can I do what I'm doing?
b.- How should I declare it to be visible from the code where the object is programmed (3rd file)? or
c.- How does the reference from the 3rd file?

c++ struct

asked by HGT 25.10.2017 в 04:01

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score 0 · Accepted Answer

Your problem is clearly indicated in the error you receive:

"identifier stXXX is undefined"

I translate it:

"el identificador stXXX no está definido"

In C ++ the code files (normally with cpp extension) can see all the definitions that are contained in the same file or those that have been added by an inclusion ( #include ), these code files are they are also known as "Translation Units" (UdT).

The definitions of a UdT are not visible in other UdT, so if your structure stXXX is in "1er_fichero.cpp" and you use it in "3er_fichero.cpp" , the UdT of 3er_fichero will not know of the existence of what is defined in the UdT of 1st file and consequently complain that " the identifier stXXX is not defined ".

Can you do what I'm doing?

As you can see from the compilation error: No.

How should I declare it to be visible from the code where the object is programmed (3rd file)?

In 3er_fichero.cpp you must include the file in which stXXX is defined, which if I'm not wrong is 2do_fichero.hpp :

#include "2do_fichero.hpp"

int main()
{
    // ... hacer cosas ...
    return 0;
 }

How does the reference from the 3rd file?

Once the inclusion has been added, you can create instances of the stXXX object normally.