Mangled LPCTSTR string returned from a function

Question

I have two projects, A and B

Project A is compiled with:
1. Standard Windows Libraries
2. Multi-byte character set
3. NO common language support

Project B is compiled with:
1. MFC as a dynamic dll
2. Multi-byte character set
3. WITH using common language support

The following function is defined in project A:

LPCTSTR CAppProxy::DriverName(IDriverAgent *driver)  
{  
  BSTR bstr;  
  HRESULT hr = driver->get_Name(&bstr);  
  CString str = CString(bstr);  
  return(str);

}

and is called from project B using:

CString name = appProxy->DriverName(driver);

but when driver name is called, the contents of "name" are garbage

score 4 · Accepted Answer · answered Jan 12 '12 at 23:12

4

A classic mistake, you're returning a pointer to a local object which reaches the end of its lifetime at the end of the function. The stack containing the string is released and overwriten with random stuff.

More specifically, you're returning a pointer to a data structure inside the CString object which is invalidated when the CString is destroyed.

If both projects are using the same version of CString you could return one of those instead of LPCTSTR.

answered Jan 12 '12 at 23:12

Mark Ransom

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Yes I see that. I don't own the files in project B so the option of returning the CString is not available to me – Jan 12 '12 at 23:25
@AndrewS., if you have control over Project A you can change the return type. If for some reason you can't recompile Project B to adapt to the new function signature, you don't have any good options left. One bad option would be to make the CString you're returning a `static` object, which means the function is no longer thread safe. – Mark Ransom Jan 12 '12 at 23:30

Mangled LPCTSTR string returned from a function

1 Answers1