C++ containers behavior -


My question is simple when I use STL containers, do they copy the value that I have there Do you archive (using copy constructor) or not? What if I give them the alphabet (character *) instead of the letter? How do they behave? What is the guarantee that the information will be stored in the system stack instead of a heap?

Thanks for the reply.

Values ​​are stored in STL containers. If you have a vector like this: 

  class BigObject {...}; Of vector & lt; BigObject & gt; MyObjs; MyObjs.push_back (obj1); MyObjs.push_back (obj2); ...

The vector will make a copy of the object that is pushing in you. Apart from this, in the case of a vector, it can make new copies later when it is the underlying memory, so keep in mind.

The same thing is true when you have an indicator such as vector & lt; Char * & gt; - But the difference is that the value of the copied value is, the string does not indicate it. So if you have: 

  vector & lt; Char * & gt; MyStrings; Char * str = new cell [256]; // SR points remembered place sprintf (str, "Hello, buffer") at position 0x1234; MyStrings.push_back (STR); Remove [] str;

... vector will receive a copy of the indicator. The indicator will have the same value (0x1234), and since you push the pointer to delete D, your vector has a wild indicator and your code will eventually crash (after In, hopefully)

By the way, could have been unable to avoid, if you used strings instead of using four letters * then: 

  typingf vector & lt ; String & gt; Wire; Strings myStrings; MyStrings.push_back ("Hello, Buffer");

Comments

Post a Comment

Popular posts from this blog

sql - dynamically varied number of conditions in the 'where' statement using LINQ -

I am using my first project LINQ (in mvc), so maybe there's something very simple that I remember. However, a day of searching and experimenting does not work, so it works. I am trying to write a LINQ query (Linux to SQL) in which in many cases where the statement is different from an OR or an AND. We do not know how many conditions are going in the query till runtime. This search is for filter control, where the user can choose multiple criteria for filtering. Select from table where table.col = 1 or table.col = 2 or table.col = 7 .... 'Other number of conditions Before I just create the SQL query as a string, while looping over all the situations. However, it seems that there should be a good way to do this in LINQ. I tried to use Expression trees, but they had a second thought for this moment on my head, where the lambda function was to be executed inside the statement such as: values ​​for matchingRows = matchingRows for each value Where (function (row) row.c...
Read more

c++ - QtQuick: QQmlApplicationEngine failed to load component qrc:/main.qml:23 Invalid attached object assignment -

Looking at my thoughts below, am I barking the wrong tree? Or in the information given below, am I misusing the Qt API to get an error in the title? I'm trying to modify the sample to work with the default coefficic project generated from Qt Creator 3.3.0 (OpenSource). Qt 5.4.0 (GCC 4.6.1, 64bit) Based on. The first thing to look at after the code is that I stand by: The sample uses the main.cpp: qmlRegisterType & lt ; Squircle & gt; ("OpenGLUARMM", 1, 0, "Squircle"); QQuickView view; View.setResizeMode (QQuickView :: SizeRootObjectToView); View.setSource (QUrl ("QRC: ///scenegraph/openglunderqml/main.qml")); View.show (); Some name changes in my name. CPP qmlRegisterType & lt; Menuscreen & gt; ("OpenGLUnderQML", 1, 0, "Main Screen"); QQmlApplicationEngine engine; Engine.load (QUrl (QStringLiteral ("QRC: /main.qml"))); I'm not sure that the difference in using QQmlApplicationEngine...
Read more

asp.net mvc - Dynamically Generated Ajax.BeginForm -

I have a problem with ASP.NET MVC Ajax forms. I generate many Ajax form in a table such as: & Lt; Input type = "submit" name = "activity" value = "add activity" / & gt; & Lt;%}% & gt; & Lt; / TD & gt; & Lt; / TR & gt; & Lt;%}% & gt; So far so good. When I post one of those forms, it gives a partial view in a div, and in this new partial view a new Ajax Beginnform (which is not in Genesis form) This second Ajax Beginnorf is exactly like the ones I got on the table, but when I post it, I do not get the "Ajax Post", but a normal post that sends me to a new page, I do not know whether the two Ajax forms What is the reason for the difference between, why is it the "dynamically generated" Ajax form behaves like a normal HTML form? By the way, I know that I can do it in different ways using javascript, but I would like to understand whether it can only be done using MVC helplars and Ajax lib...
Read more