1

Right, having looked up this issue, I believe that it is caused because I have in my class definition wchar_t downloadedText[400000]; I have read solutions about how I should deal with this by using the new operator to assign the space, ie: wchar_t *downloadedText; downloadedText = new wchar_t[400000];

However I need to write instances of the class to a file, and assigning the variable like above appears to use pointers to point to data stored in a way that does not get written to my file. It is this same reason why I cannot use std::vector.

I have read that another option I may have is that I can increase the size of the 'stack'. I use VS2010 as my IDE, and I located in my project properties > Linker > System 'Stack Commit Size', 'Stack Reserve Size', 'Heap Commit Size' and 'Heap Reserve Size' fields, but I am unsure if this is how I can deal with my issue, and if it is, what to correctly set the appropriate fields to.

Improve this question
14
  • 1
    How are you accessing the element to write in each case? Commented May 3, 2012 at 2:13
  • 4
    Could you update your question with a code sample of the writing process for static arrays vs. pointer/vector? Commented May 3, 2012 at 2:16
  • 2
    fileOutput.write(reinterpret_cast<char *> (&myObjects[i]), sizeof(MyClass)); The process of writing to the file does not change when changing the members of the class (although if I wanted to read object data from the file after adding/removing member variables I would be unable to do so). I obviously cannot use std::vector in the same way that I cannot use std::string because they do not directly contain the data I want to write, instead they are more complex and contain pointers to the actual data I want, etc. Commented May 3, 2012 at 2:21
  • 1
    how do you write when you have pointer? Commented May 3, 2012 at 2:22
  • 2
    Why not to write a proper write/serialization function, or simply use some serialization library? stackoverflow.com/questions/234724/how-to-serialize-in-c Commented May 3, 2012 at 4:05

4 Answers 4

Reset to default
3

If you must do it this way... You could just write the array explicitly, after writing out the object. eg.

write((char*)&myObjects[i]), sizeof(MyClass));
write((char*)downloadedText, sizeof(downloadedText[0]) * 400000);

And to read it back in:

read((char*)&myObjects[i]), sizeof(MyClass));
downloadedText = new wchar_t[400000];
read((char*)downloadedText, sizeof(downloadedText[0]) * 400000);

However, this is very fragile and prone to errors. Overwriting objects in memory as done by the read is at best bad form except perhaps if you're using a struct created explicitly for that purpose which would typically contain only PODs. As a minimum, note that you have to set the downloadedText member field after the read writes over it.

Improve this answer
Sign up to request clarification or add additional context in comments.

1 Comment

My class does only contain PODs. In addition I would prefer to keep downloadedText as a member variable of said class.
2

You can allocate the whole object with new operator in system heap but not on stack. In this case you can write this object to file in the same manner and have no troubles with stack overflow.

Improve this answer

3 Comments

I thought of this too, however it does not like the statement myObjects.push_back(new MyClass(0,0,TEXT("text\0"))); It gives me an error along the lines of error C2664: 'void std::vector<_Ty>::push_back(_Ty &&)' : cannot convert parameter 1 from 'MyClass*' to 'MyClass &&' 1> with 1> [ 1> _Ty=MyClass 1> ] 1> Reason: cannot convert from 'MyClass *' to 'MyClass' 1> No constructor could take the source type, or constructor overload resolution was ambiguous
That error message means that myObjects is a std::vector<MyClass>, which you'll need to change to std::vector<MyClass*>.
Thinking more about this, if you put your objects into a std::vector<MyClass>, then they're already allocated on the heap and off the stack.
1

Yes, you can increase the stack size in Visual Studio with the linker option /STACK. This linker option is also editable with the project properties Stack Reserve Size and Stack Commit Size. It is enough to set the reserve size, the commit size is optional. Nevertheless you should also be able to use std::vector.

Improve this answer

1 Comment

I did initially try this without any success. However I then set it to a more insane value of 1024000000 (1GB?) as I didn't realise it appeared to be requesting a figure in bytes. I cannot write std::vector class members to my file because it is not POD. Unfortunately I can only store around 120 entries before getting some sort of bad alloc error. In addition it starts using a fair amount of memory, which is a little annoying as I'd prefer it to not use the memory for all 400000 characters unless it has to. ie if I'm not storing anything it should hopefully be taking little memory.
0

It sounds like you're fine with your current serialization strategy (make the object POD, and write it as a POD value). In that case, your question really is "how can a keep these objects from taking up too much space on the stack?" The answer: don't put them on the stack.

Allocate them with new. Or, preferably, wrap them in smart pointers of some kind.

You have string-like data. It so happens that C++ offers a string class. In fact, since you're talking about wchar_t characters, you want to look at std::wstring (in the <string> header).

Improve this answer

3 Comments

I cannot use std::string as a class member because it is not POD. I will have issues trying to write it to the file in binary mode.
You'll only have issues if you try to write the containing struct or class to the file as if it's POD. If you write each element separately, it's trivial to use std::wstring.
I can write instances of my object just fine provided it's got only POD types like int, char, etc, and arrays declared with their exact length in the class, ie char myArray[200] Trying to write ONLY an std::string or std::wstring does not work because they do not themselves contain the data I want, they contain pointers to it, etc.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.