Most of the MFC programmers has tendency to declare the global const CString objects instead of global const char* array (or LPCTSTR) as string constants.
To optimize the storage of constant data, you have to make sure that the constant data is always get stored with your program. Before going to CString specific issues, let’s go take some other examples.
If you want it to be a constant, you must declare it as an initialized const static or global variable as follows. (If no const specified there, it will not be stored with your program)
[sourcecode language='cpp']
const char g_pch[] = “test”;[/sourcecode]
If several instances of your program are running, the same EXE and DLL files will be mapped to each process’s virtual address space. To know what’s happening inside and to
| Name | Type | Access | Contents |
| .text | Code | Read-only | Program code |
| .rdata | Data | Read-only | Constant initialized data |
| .data | Data | Read/write | Non-constant initialized data |
| .bss | Data | Read/write | Non-constant uninitialized data |
The g_pch data we mentioned before will be stored under .rdata section which is part of the program. it’s happened because the data is constant (declared as const).
The linker will put the built in types and even structures as global constant as part of programs. But the case is different for C++ objects. C++ objects should be initialized using constructors, thus the compiler will generate code for constructors and destructors. Take the following example
[sourcecode language='cpp']
const CRect g_rect(0, 0, 100, 100);
[/sourcecode]
[sourcecode language='cpp']
const CString g_str(“Hello World!”);
[/sourcecode]
In this case the CString object will be put inside the .bss section and there’s a constant string which we passed to the constructor. It will be stored under .data section (as we have not specified it as const). In addition to that, CString objects are keeping data by dynamically allocating memory in the heap. To optimize the storage of constant data, it’s always better to declare strings are const char* or if your program wants to support both UNICODE and non-UNICODE build, then delcare it as
[sourcecode language='cpp']LPCTSTR g_pch = _T(“Hello World”);[/sourcecode]
So take care of Global CString constants. I got this nice tip from the book “Programming Visual C++” by David J. Kruglinski