Thread: space in string

Hello everyone,


The space in string should use heap address memory space, not stack, right? But through debugging, for example,

Code:

string str = "hello";

why I can not see the invocation of new operator? Anyone could point out where STL string class allocates space on heap and using which function to allocate please (any other approach other than using new to allocate space on heap?)?


thanks in advance,
George

Some string implementations keep a small buffer (like maybe 16 bytes) for short strings to avoid dynamically allocating small buffers.

Try it with a string more than 16 characters. If that doesn't work, keep adding to the string in a loop, eventually it will have to allocate memory. If that doesn't work, you aren't trapping the allocation properly.

If you look through the <string> header file (& whatever implementation specific headers it includes) I'm sure you'll find some places where it calls new. Probably deep in the bowels of the STL...

Thanks everyone,


I find Daved and CornedBee are correct. The related code is in xmemory and xstring. I want to share my findings with you here and let you comment if you think I am correct or not. :-)

1. For small buffer, will use 16-bytes stack array;
2. For large buffer, will use allocator to allocate space on heap.

Here are the related code in class string,

Code:

	union _Bxty
		{	// storage for small buffer or pointer to larger one
		_Elem _Buf[_BUF_SIZE];
		_Elem *_Ptr;
		} _Bx;

Originally Posted by CornedBee

No, you won't. std::string only calls its allocator's allocate() function. You'll have to look for std::allocator to find the new call.

regards,
George

Please note that that information is really only useful if we know what compiler and standard library you are using, since implementations vary (especially for the string class).

Hi Daved and Elysia,

Originally Posted by c

It's Microsoft Visual C++. 2008 I think?

Yes, it is Visual Studio 2008. I like to try new things.


regards,
George