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Editorial Team
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Asked: 2026-05-15T11:49:20+00:00

In Qt’s qrect.h I found class declaration starting like this: class Q_CORE_EXPORT QRect {

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In Qt’s qrect.h I found class declaration starting like this: 

class Q_CORE_EXPORT QRect {
};

As you can see there are two identifiers after class keyword. How shall I understand this?
Thank you.

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1 Answer

  1. Editorial Team

    Q_CORE_EXPORT is a macro that gets expanded to different values depending on the context in which it’s compiled.

    A snippet from that source:

    #ifndef Q_DECL_EXPORT
#  ifdef Q_OS_WIN
#    define Q_DECL_EXPORT __declspec(dllexport)
#  elif defined(QT_VISIBILITY_AVAILABLE)
#    define Q_DECL_EXPORT __attribute__((visibility("default")))
#  endif
#  ifndef Q_DECL_EXPORT
#    define Q_DECL_EXPORT
#  endif
#endif
#ifndef Q_DECL_IMPORT
#  ifdef Q_OS_WIN
#    define Q_DECL_IMPORT __declspec(dllimport)
#  else
#    define Q_DECL_IMPORT
#  endif
#endif

// ...

#    if defined(QT_BUILD_CORE_LIB)
#      define Q_CORE_EXPORT Q_DECL_EXPORT
#    else
#      define Q_CORE_EXPORT Q_DECL_IMPORT
#    endif

    Those values (__declspec(dllexport), __attribute__((visibility("default"))), etc.) are compiler-specific attributes indicating visibility of functions in dynamic libraries.

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