Q$2.($a$)$ What is the difference between a statically linked library $($or $$archive$)$ and

a dynamically linked library $($or $$shared object$)?$ State the advantages and

disadvantages of each. For each type of library, give an example where it would

be the preferred choice. $[8]$

Scrutinise the code for a small library given in Figure Q$2.$ Throughout this question,

line numbers are included only for ease of reference and do not constitute part of

the program.

$($b$)$ What would happen if a source file accidentally included the header file twice?

Suggest and enhancement to overcome this problem. $[5]$

The following small program is written which uses this library:

$1$ #include

$2$ #include "apse.h$"$

$3$ int main$()$

$4\{$

$5$ One one;

$6$ Counter c$($one$.$get$())$;

$7$ std::cout $<<$ c$.$get$()<<\text{'}\text{'}<<$ c$.$get$()<<$ std::endl;

$8$ return $0$;

$9\}$

Object files are produced from the source files, and a shared library is created using

the command

g$++-$fPIC $-$shared one.o counter.o $-$o libapse.so

The main program $($called try$)$ is then linked using the command

g$++-$o try main.o $-$L$.-$lapse

$($c$)$ Why is the compiler option $-$fPIC necessary when building the shared library?

$[4]$

$($d$)$ What is the function of the $-$L$.$ option in building the program? $[4]$

$($e$)$ Running the program with $./$try produces the message

$./$try: error while loading shared libraries: libapse.so: cannot

open shared object file: No such file or directory.

However, the file libapse.so exists in the build directory. What is the remedy

for this? $[4]$

Page $4$ of $13/$OVER

$1//$ File: apse.h

$2$ struct One $\{$

$3$ int get$($void$)$;

$4\}$;

$5$

$6$ class Counter $\{$

$7$ public:

$8$ Counter$($int start$=0)$;

$9$ int get$($void$)$;

$10$ private:

$11$ int i;

$12\}$;

$1//$ File: apse$1.$cxx

$2$ #include "apse.h$"$

$3$ int One::get$($void$)\{$ return $1$; $\}$;

$1//$ File apse$2.$cxx

$2$ #include "apse.h$"$

$3$ Counter::Counter$($int start$)$ : i $\{$start$\}\{\}$

$4$ int Counter::get$($void$)\{$ return i$++$; $\}$

Figure Q$2$: Source code for the apse library