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C++C++ - Tutorial 005. Pointers, Arrays and Loops

July 6, 2017, 2:40 a.m.

C++, pointer, arrays, loops

An array of elements of type char can be declared like this:

char v[6];  // array of 6 characters

Similarly, a pointer can be declared like this:

char* p; // pointer to character

In declarations, [] means ‘‘array of’’ and *means ‘‘pointer to.’’ All arrays have0as their lower bound, so v has six elements, v[0] to v[5] . The size of an array must be a constant expression. A pointer variable can hold the address of an object of the appropriate type:

char∗ p = &v[3]; // p указывает на четвёртый элемент массива v
char x = ∗p; // *p является объектом, на который указывает p

In an expression, prefix unary ∗ means ‘‘contents of’’ and prefix unary & means ‘‘address of.’’ We can represent the result of that initialized definition graphically:

QMLQML - Lesson 023. The hunt for bugs in the transmission pointer to QObject in QML

One of the most vile and little predictable bugs are those that arise in an uncertain time. Among these include a bug that appears when the pointer is transmitted to the QObject in QML layer. The problem is that if there is no parent QObject, the transmission layer occurs in QML object change of ownership, that is, it is set JavaScriptOwnership. As a result, when the QML layer lost all references to this object, it will be removed garbage collector QML. Accordingly, all references in C++ layer will be non-valid. And the app when trying to appeal to these links will collapse in silence, without saying anything about the cause of the collapse.

Speaking of response uncertainty bug, it should be noted that this uncertainty stems from the time of garbage collection. In a typical embodiment, the time may come when the program a couple of gigabytes of memory dine or when the memory is not enough, and it will be available by performing garbage collection. That is, the application can run without problems for a long time without causing a bug, and it is even possible to go through several versions before the bug will manifest itself at any user who decides to report it to the developers.

It is worth noting that this rule will not be applied to the objects declared as Q_PROPERTY .

But we can use QML function gc() to show the problem, which will accelerate the garbage collection.

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May 29, 2020, 2:32 p.m.
glushchenkoin

C ++ - Test 004. Pointers, Arrays and Loops

  • Result:40points,
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AS
May 26, 2020, 11:29 a.m.
Artem Sun-Dun-Chan

C ++ - Test 004. Pointers, Arrays and Loops

  • Result:50points,
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May 25, 2020, 11:33 a.m.
Mitja Nagibin

C ++ - Test 004. Pointers, Arrays and Loops

  • Result:50points,
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