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std::queue class->struct->union. struct not initalized ?

Started by XBog Sep 23, 2012 at 3:23 PM 4 replies 1.3k views

Original Post

Sep 23, 2012 at 3:23 PM

Hello,

i have a problem i dont understand.

I have a class Test with a struct teststr and use union for the struct.

[source lang="cpp"]#include

class Test
{
struct teststr
{
bool test;
};

union
{
teststr size;
};
};[/source]

In the main i want too push the Test object in the queue.

[source lang="cpp"]std::queue m_tests; ///< Queue of available tests
Test test1; //test1.teststr.test is null/empty????
Test test2; //test2.teststr.test is null//empty ??[/source]
The problem is that the test1 var ist initialized but not the struct within ????
So here test1.teststr.test is empty.

If i set Test test1; before the queue the struct is initialized so test1.teststr.test is filled.

[source lang="cpp"]Test test1; //.teststr.test is filled !!
std::queue m_tests; ///< Queue of available tests
Test test2; //test2.teststr.test is filled !![/source]

So my question is:
why is the struct teststr not initialized/set if use the following order?

[source lang="cpp"]std::queue m_tests; ///< Queue of available tests
Test test1; //test1.teststr.test is null/empty????
Test test2; //test2.teststr.test is null//empty ??;[/source]

Trienco

Sep 24, 2012 at 4:31 AM

Considering that your class has no constructor with an initializer list and you don't seem to initialize anything at any point in your code, why do you expect anything to be initialized?

The only reason you think it is "filled" is because it just randomly happens to contain what you want. Unless YOU initialize your stuff, it will contain random garbage.

XBog

Sep 24, 2012 at 5:04 PM

test.size.test should contain true or false. test holds an object so i don't have to call constructor or have to initialize something, right? ...

i talked to my workmate today. and he confirmed the problem ... we don't know why test.size.test is empty, but it should filled with true or false (garbage)

u just have to test the same order:

[source lang="cpp"]std::queue m_tests; ///< Queue of available tests
Test test1; //test1.teststr.test is null/empty????
Test test2; //test2.teststr.test is null//empty ??[/source]

attached a screenshot of it ....

Bregma

Sep 24, 2012 at 5:53 PM

test.size.test should contain true or false.

True. It's a bool, it will contain either true or false. False is zero, true is anything else.

test holds an object so i don't have to call constructor or have to initialize something, right? ...
[/quote]
False. As a general rule, if you want something initialized, you must initialize it, otherwise it's not initialized.

i talked to my workmate today. and he confirmed the problem ... we don't know why test.size.test is empty, but it should filled with true or false (garbage)
[/quote]
I guarantee test.size.test is not "empty" and contains garbage. If whatever tool you're using to show its contents show nothing, it is likely that your tool is wither not working the way you think it's working, or it's broken.

An uninitialized variable is uninitialized. If you want a variable to have a known value, you must give it a known value.

XBog

Sep 24, 2012 at 6:07 PM

hmmm .. ok .. seems to be a bug in visual studio?

Added an integer and visual studio 2010 just shows some ??? but my console output shows the right value .....

Edit: Ok not even a bug ... With unions i have to initialize one member of Union at any rate sry my fault

Trienco

Sep 25, 2012 at 4:45 AM

And make sure you're not debugging a release build or nothing you see can really be trusted.

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