Set - 3

Question 11 :

How do you print an address ?

Answer :

The safest way is to use printf() (or fprintf() or sprintf()) with the %P specification. That prints a void pointer (void*). Different compilers might print a pointer with different formats.

Your compiler will pick a format that's right for your environment. 
If you have some other kind of pointer (not a void*) and you want to be very safe, cast the pointer to a void*:

printf( %Pn, (void*) buffer );

 


Question 12 :

Can a file other than a .h file be included with #include ?

Answer :

The preprocessor will include whatever file you specify in your #include statement. Therefore, if you have the line

#include

in your program, the file macros.inc will be included in your precompiled program. It is, however, unusual programming practice to put any file that does not have a .h or .hpp extension in an #include statement.

You should always put a .h extension on any of your C files you are going to include. This method makes it easier for you and others to identify which files are being used for preprocessing purposes.

For instance, someone modifying or debugging your program might not know to look at the macros.inc file for macro definitions. That person might try in vain by searching all files with .h extensions and come up empty.

If your file had been named macros.h, the search would have included the macros.h file, and the searcher would have been able to see what macros you defined in it.


Question 13 :

What is Preprocessor ?

Answer :

The preprocessor is used to modify your program according to the preprocessor directives in your source code.

Preprocessor directives (such as #define) give the preprocessor specific instructions on how to modify your source code. The preprocessor reads in all of your include files and the source code you are compiling and creates a preprocessed version of your source code.

This preprocessed version has all of its macros and constant symbols replaced by their corresponding code and value assignments. If your source code contains any conditional preprocessor directives (such as #if), the preprocessor evaluates the condition and modifies your source code accordingly.

The preprocessor contains many features that are powerful to use, such as creating macros, performing conditional compilation, inserting predefined environment variables into your code, and turning compiler features on and off.

For the professional programmer, in-depth knowledge of the features of the preprocessor can be one of the keys to creating fast, efficient programs.


Question 14 :

How can you restore a redirected standard stream ?

Answer :

The preceding example showed how you can redirect a standard stream from within your program. But what if later in your program you wanted to restore the standard stream to its original state?

By using the standard C library functions named dup() and fdopen(), you can restore a standard stream such as stdout to its original state.

The dup() function duplicates a file handle. You can use the dup() function to save the file handle corresponding to the stdout standard stream.

The fdopen() function opens a stream that has been duplicated with the dup() function.


Question 15 :

What is the purpose of realloc( ) ?

Answer :

The function realloc(ptr,n) uses two arguments. the first argument ptr is a pointer to a block of memory for which the size is to be altered. The second argument n specifies the new size.

The size may be increased or decreased. If n is greater than the old size and if sufficient space is not available subsequent to the old region, the function realloc( ) may create a new region and all the old data are moved to the new region.