global variable in an mfc application ??

[Amilisoft]

where can i declare a global variable to use it in different classes. thanks

[Andreas Masur]

Global variables need to be declared in the header and be defined in one .cpp file...e.g.

// global.hpp
extern int iInt;

// global.cpp
int iInt;

However, usually you would avoid using globals...why do you need one in the first place?

[ravirams]

in afxstud.h

CString str1;


then use as

extern CString str1; where ever u want( other classes);

*** enjoy in programming***

[x8086]

ravirams ,
i am using connection variable in a way you said
but i am getting following errors

Linking...
DataBaseView.obj : error LNK2005: "class _com_ptr_t<class _com_IIID<struct _Connection,&struct __s_GUID _GUID_00000550_0000_0010_8000_00aa006d2ea4> > pConnection" (?pConnection@@3V?$_com_ptr_t@V?$_com_IIID@U_Connection@@$1?_GUID_00000550_0000_0010_8
000_00aa006d2ea4@@3U__s_GUID@@A@@@@A) already defined in DataBase.obj
DBFunctions.obj : error LNK2005: "class _com_ptr_t<class _com_IIID<struct _Connection,&struct __s_GUID _GUID_00000550_0000_0010_8000_00aa006d2ea4> > pConnection" (?pConnection@@3V?$_com_ptr_t@V?$_com_IIID@U_Connection@@$1?_GUID_00000550_0000_0010_80
00_00aa006d2ea4@@3U__s_GUID@@A@@@@A) already defined in DataBase.obj
Debug/DataBase.exe : fatal error LNK1169: one or more multiply defined symbols found
Error executing link.exe.

x8086

[trickyg]

ravirams ,
i am using connection variable in a way you said
but i am getting following errors

x8086

What is your variable name?

From the error messages you showed us, it could be caused by "multiple declaration of variable".

All "extern" statements can be included in all ".h" or ".cpp":

// global.hpp
extern int iInt; 

But there must be one normal declaration in either ONE (and only one) ".cpp" or in a ".h" in which the contents are used by only one ".cpp":

// global.cpp
int iInt; 

if the normal declaration is made in a ".h" file, and this file is included by a ".h" that is included by many ".cpp", you will also get the same error.

[Ajay Vijay]

Let it be simple:

• You declare as variable as extern many times, as many times you wish to refer in source files.
• You define the variable only once across all source files.

Defining let the linker (not the compiler) put the variable into executable, at global level. If you 'define' a variable many times, linker will already find in other object file (since you may have defined in the respective source file) and will compain you the same.

[trickyg]

As pointed out by Ajay Vijay, there are differences between declaration and definition, which I overlooked and probably messed up in my previous post, I am sorry about my misleading post, please refer to Ajay Vijay's post which is more precise and neat.

p/s: thank you, Ajay Vijay