<QtCompilerDetection> - Compiler-specific Macro Definitions

Defined if the application is compiled using Borland/Turbo C++.

Defined if the application is compiled using Reliant C++.

Defined if the application is compiled using Clang.

Defined if the application is compiled using Comeau C++.

Defined if the application is compiled using DEC C++.

Defined if the application is compiled using Edison Design Group C++.

Defined if the application is compiled using Green Hills Optimizing C++ Compilers.

Defined if the application is compiled using GNU Compiler Collection (GCC).

Defined if the application is compiled using MetaWare High C/C++.

Defined if the application is compiled using HP aC++.

Defined if the application is compiled using KAI C++.

Defined if the application is compiled using MIPSpro C++.

Defined if the application is compiled using Microsoft Visual C/C++, Intel C++ for Windows.

Defined if the application is compiled using CenterLine C++.

Defined if the application is compiled using Portland Group C++.

Defined if the application is compiled using Forte Developer, or Sun Studio C++.

Defined if the application is compiled using Digital Mars C/C++ (used to be Symantec C++).

Defined if the application is compiled using SCO OUDK and UDK.

Defined if the application is compiled using Watcom C++.

Enforces constant initialization when supported by the compiler.

If the compiler supports the C++20 constinit keyword, Clang's [[clang::require_constant_initialization]] or GCC's __constinit, then this macro expands to the first one of these that is available, otherwise it expands to nothing.

Variables marked as constinit cause a compile-error if their initialization would have to be performed at runtime.

For constants, you can use constexpr since C++11, but constexpr makes variables const, too, whereas constinit ensures constant initialization, but doesn't make the variable const:

This macro was introduced in Qt 6.4.

This macro marks a symbol for shared library export (see Creating Shared Libraries).

II-21-1. See Also▲

This macro declares a symbol to be an import from a shared library (see Creating Shared Libraries).

II-22-1. See Also▲

Can be used in switch statements at the end of case block to tell the compiler and other developers that that the lack of a break statement is intentional.

This is useful since a missing break statement is often a bug, and some compilers can be configured to emit warnings when one is not found.

II-23-1. See Also▲

Expands to a string that describe the function the macro resides in. How this string looks more specifically is compiler dependent. With GNU GCC it is typically the function signature, while with other compilers it might be the line and column number.

Q_FUNC_INFO can be conveniently used with qDebug(). For example, this function:

template<typename TInputType>
const TInputType &myMin(const TInputType &value1, const TInputType &value2)
{
    qDebug() << Q_FUNC_INFO << "was called with value1:" << value1 << "value2:" << value2;

    if(value1 < value2)
        return value1;
    else
        return value2;
}

when instantiated with the integer type, will with the GCC compiler produce:

const TInputType& myMin(const TInputType&, const TInputType&) [with TInputType = int] was called with value1: 3 value2: 4

If this macro is used outside a function, the behavior is undefined.

Hints to the compiler that the enclosed condition, expr, is likely to evaluate to true.

Use of this macro can help the compiler to optimize the code.

Example:

    // the condition inside the "if" will be successful most of the times
    for (int i = 1; i <= 365; i++) {
        if (Q_LIKELY(isWorkingDay(i))) {
            ...
        }
        ...
    }

II-25-1. See Also▲

Hints to the compiler that the enclosed condition, expr, is likely to evaluate to false.

Use of this macro can help the compiler to optimize the code.

Example:

bool readConfiguration(const QFile &file)
{
    // We expect to be asked to read an existing file
    if (Q_UNLIKELY(!file.exists())) {
        qWarning() << "File not found";
        return false;
    }

    ...
    return true;
}

II-26-1. See Also▲

III-1-1. Q_CC_INTEL▲

III-1-2. Q_DECL_CONSTEXPR▲

III-1-3. Q_DECL_FINAL▲

    // more-derived classes no longer permitted to override this:
    virtual void MyWidget::paintEvent(QPaintEvent*) final;

    class QRect final { // cannot be derived from
        // ...
    };

III-1-4. Q_DECL_NOEXCEPT▲

III-1-5. Q_DECL_NOEXCEPT_EXPR(x)▲

III-1-6. Q_DECL_NOTHROW▲

III-1-7. Q_DECL_OVERRIDE▲

    // generate error if this doesn't actually override anything:
    virtual void MyWidget::paintEvent(QPaintEvent*) override;

III-1-8. Q_DECL_RELAXED_CONSTEXPR▲