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QFlags tutorial: Difference between revisions

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[[Category:snippets]]
[[Category:snippets]]


[toc align_right="yes" depth="3"]
= Simple tutorial for safe-usage QFlags =


== Overview ==
== Overview ==


First of all we should write about macro <code>Q_FLAGS</code>
First of all we should write about the macro:
<code>Q_FLAGS</code>
''This macro registers one or several flags types to the meta-object system''
''This macro registers one or several flags types to the meta-object system''


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== Usage sample ==
== Usage sample ==


</code>void test (TestClass::Options flag)
<code>void test (TestClass::Options flag)
{
{
  if (flag.testFlag(TestClass::OptionA))
  if (flag.testFlag(TestClass::OptionA))
Line 51: Line 49:
  test (TestClass::OptionA | TestClass::OptionB);
  test (TestClass::OptionA | TestClass::OptionB);
  test (0x1); // error
  test (0x1); // error
}<code>
}</code>


<code>testFlag(flag)</code> method checks if flag is set in <code>QFlags</code>.
The <code>testFlag(flag)</code> method checks if flag is set in <code>QFlags</code>.


=== Some example ===
=== Some examples ===


</code>TestClass::Options f1(TestClass::OptionA | TestClass::OptionB); // 000011
<code>TestClass::Options f1(TestClass::OptionA | TestClass::OptionB); // 000011
TestClass::Options f2(~f1); // 111100
TestClass::Options f2(~f1); // 111100
TestClass::Options f3(Foo::OptionA | Foo::OptionC); // 000101
TestClass::Options f3(Foo::OptionA | Foo::OptionC); // 000101
TestClass::Options f4(f1^f3); // 000110
TestClass::Options f4(f1^f3); // 000110
</code>

Revision as of 01:14, 7 April 2015

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Overview

First of all we should write about the macro:

Q_FLAGS

This macro registers one or several flags types to the meta-object system

Example:

class TestClass
 {
 public:
 enum Option {
 OptionA = 1, // 000001
 OptionB = 2, // 000010
 OptionC = 4, // 000100
 OptionD = 8, // 001000
 OptionE = 16, // 010000
 OptionF = 32 // 100000
 // … some more options with value which is a power of two
 };
 Q_DECLARE_FLAGS(Options, Option)
 };

Q_DECLARE_OPERATORS_FOR_FLAGS(TestClass::Options)

The

Q_DECLARE_FLAGS()

macro expands to

typedef QFlags<Enum> Flags;<code> In our case it expandes to <code>typedef QFlags<Option> Options;

where Option - is an enum name, and Options - is name for set of flags. The

Q_DECLARE_OPERATORS_FOR_FLAGS()

macro declares global

operator|()

functions for Flags, which is of type

QFlags<T>

. The

Q_DECLARE_FLAGS()

macro does not expose the flags to the meta-object system, so they cannot be used by Qt Script. To make the flags available for these purpose, the

Q_FLAGS()

macro must be used.

Usage sample

void test (TestClass::Options flag)
{
 if (flag.testFlag(TestClass::OptionA))
 qDebug() << "A";
 if (flag.testFlag(TestClass::OptionB))
 qDebug() << "B";
}

int main()
{
 test (TestClass::OptionA | TestClass::OptionB);
 test (0x1); // error
}

The

testFlag(flag)

method checks if flag is set in

QFlags

.

Some examples

TestClass::Options f1(TestClass::OptionA | TestClass::OptionB); // 000011
TestClass::Options f2(~f1); // 111100
TestClass::Options f3(Foo::OptionA | Foo::OptionC); // 000101
TestClass::Options f4(f1^f3); // 000110