Conditional inclusion of header files

Ram (one of my peers, name changed) complained that he was unable to create an object of class (say clsX).

We have the practise of having our class declarations in header files. So the declaration of the class clsX was in X.h file.

To define an object of class clsX in a soure file, Ram had included the header file X.h in the source file. Despite that he was unable to define the object of class clsX. He got compiler error for the same.

Ram complained Ravi (one of my peers, name changed) that he was unable to create an object of class clsX. Ravi is the one who wrote the class clsX.

Ravi worked on it to provide the following report:

1. I am not sure about why this problem is occurring, but it seems to be because of some issue with C++ compilers, as mentioned in these two posts I found for the error C2143 -
1. http://sabbour.wordpress.com/2006/12/30/error-c2143-syntax-error-missing-before/
2. http://www-subatech.in2p3.fr/~photons/subatech/soft/carnac/CPP-INC-1.shtml
2. I tried moving the class declaration to the source file, and then removed the header file inclusion. The problem was resolved, which means the contents of the header file 'clsX.h' do not have any syntax error.
3. I removed the inclusion of the header file 'clsX.h' and instead used a forward declaration as follows, and this solution worked fine.
4. Please use a forward declaration for the class clsTable, as mentioned in point 3 above, to continue your analysis. I shall look into the problem further to ascertain the root cause.

I decided to have a hand on the problem under discussion. By seeing the compiler error, I got that the declaration of the class clsX didn't reach the source file despite the inclusion of header file X.h.

We use preprocessor directives to conditionally include a header file content into other source file. This is to avoid the duplication of declarations.

On checking the macro that is used along with the preprocessor directives in X.h, I found that the macro used is already defined in some other header file (say Y.h). The header file Y.h is already included in the source file in which X.h is also included. Because of which the macro defined in Y.h eliminated the inclusion of X.h contents.

I.e.

Y.h
 #ifndef _Y_H
 #define _Y_H
 ...
 ...
 #endif

X.h
 #ifndef _Y_H
 #define _Y_H
 declaration of class clsX
 #endif

Z.c
 #include "../Y/Y.h"
 #include "../X/X.h"
 define object of class clsX

Here you can see that the contents of header file X.h (I.e. declaration of class clsX), won't be included. This is because the contents of header file X.h would be included in file Z.c only if the macro _Y_H is not defined before. But macro _Y_H is already defined in Z.c by the inclusion of header file Y.h.

I pointed out the mistake of using the same macro for two header files which solved the problem.

Sharing files/folders to Windows clients from linux (Ubuntu)

Right click the folder that needs to be shared. Select the option 'Sharing Options'. The file manager window gets open.

Enable 'Share this folder'. On doing so, if the sharing service is not installed the following window will appear.

Press the button "Install service". It will install the SMB service.

After successful installation, it will ask to retsart your session.

Press the button "Restart session".

And now add a SMB user. To do so, open the terminal in Ubuntu and type the following command.

 sudo smbpasswd -a username

This will ask for the new SMB password for the username given. Provide the SMB password. After successful addition of SMB user, the shared folder can be accessed from the windows client using the username and password created.

End Of Line (EOL) in Linux and Windows

The end of a line of text is marked by the EOL character. The EOL character differs between Windows and Linux.

In Linux, the EOL character is line feed (LF) character '\n'. Whereas in Windows, the EOL character is carriage return (CR) character '\r' followed by the line feed (LF) character '\n'.

For example, create a text file containing the following in both Linux (LinuxSampleTxtDocument.txt) and Windows (WindowsSampleTxtDocument.txt).

 this is first line
 this is second line
 this is third line

And dump the contents of both the files.

sh-3.1$ hexdump -cb LinuxSampleTxtDocument.txt
0000000   t   h   i   s       i   s       f   i   r   s   t       l   i
0000000 164 150 151 163 040 151 163 040 146 151 162 163 164 040 154 151
0000010   n   e  \n   t   h   i   s       i   s       s   e   c   o   n
0000010 156 145 012 164 150 151 163 040 151 163 040 163 145 143 157 156
0000020   d       l   i   n   e  \n   t   h   i   s       i   s       t
0000020 144 040 154 151 156 145 012 164 150 151 163 040 151 163 040 164
0000030   h   i   r   d       l   i   n   e  \n
0000030 150 151 162 144 040 154 151 156 145 012
000003a

sh-3.1$ hexdump -cb WindowsSampleTxtDocument.txt
0000000   t   h   i   s       i   s       f   i   r   s   t       l   i
0000000 164 150 151 163 040 151 163 040 146 151 162 163 164 040 154 151
0000010   n   e      \r  \n   t   h   i   s       i   s       s   e   c
0000010 156 145 040 015 012 164 150 151 163 040 151 163 040 163 145 143
0000020   o   n   d       l   i   n   e  \r  \n   t   h   i   s       i
0000020 157 156 144 040 154 151 156 145 015 012 164 150 151 163 040 151
0000030   s       t   h   i   r   d       l   i   n   e
0000030 163 040 164 150 151 162 144 040 154 151 156 145
000003c