|
|
| Line 1: |
Line 1: |
| {{TOCright}}
| | #REDIRECT [[ist:Make/CVS example 1]] |
| == The Problem (in Portuguese) ==
| |
| | |
| Considere quatro ficheiros <tt><span style="color: #990000">recurs.cpp</span></tt> (contendo a função <tt><span style="color: #990000">factrecurs</span></tt>), <tt><span style="color: #990000">recurs.h</span></tt> (contendo a declaração da função <tt><span style="color: #990000">factrecurs</span>),</tt> <tt><span style="color: #990000">iter.cpp</span></tt> (contendo a função <tt><span style="color: #990000">factiter</span> </tt>), <tt><span style="color: #990000">iter.h</span></tt> (contendo a declaração da função <tt><span style="color: #990000">factiter</span>)</tt> e <tt><span style="color: #990000">main.cpp</span></tt> (contendo a função <tt><span style="color: #990000">main</span></tt> que invoca sequencialmente ambas as funções anteriores e que inclui <tt><span style="color: #990000">recurs.h</span></tt> e <tt><span style="color: #990000">iter.h</span></tt>).
| |
| | |
| # Construa, com estes cinco ficheiros, um projecto designado <strong>factorial</strong>, indicando os comandos para o colocar sob o controlo de versões do CVS. Admita que o repositório já existe em <tt><span style="color: #990000">/cvs</span></tt>.
| |
| # Construa uma <tt><span style="color: #990000">Makefile</span></tt> para gerar o executável <tt><span style="color: #990000">fact</span></tt>, a partir dos ficheiros anteriores. Indique os comandos necessários para colocar a <tt><span style="color: #990000">Makefile</span></tt> no repositório CVS.
| |
| # Considere agora que vai ter dois executáveis, cada um invocando a sua função. Indique as alterações à <span style="color: #990000"> <tt>Makefile</tt></span> para que passe a gerar os executáveis <tt><span style="color: #990000">recurs</span></tt> e <tt><span style="color: #990000">iter</span></tt>, utilizando ambos o mesmo ficheiro <tt><span style="color: #990000">main.cpp</span></tt> (mas diferentes implementações do factorial). Indique as operações do CVS para criar a nova versão do projecto, assumindo que o projecto está checked-out no directório corrente.
| |
| # Considere uma nova versão do projecto: pretende-se construir um único executável <span style="color: #990000"> <tt>fact</tt></span>, mas a escolha da implementação do factorial é efectuada em tempo de execução. Considere que os ficheiros <tt><span style="color: #990000">recurs.cpp</span></tt> e <tt><span style="color: #990000">recurs.h</span></tt> existem num subdirectório <tt><span style="color: #990000">recurs</span></tt> e, analogamente, existe um directório <tt><span style="color: #990000">iter</span></tt> para a outra versão. Cada um dos conjuntos apresenta agora a mesma interface para a função que calcula o factorial: <tt><span style="color: #990000">fact</span></tt>. Construa duas bibliotecas dinâmicas, ambas designadas por <span style="color: #990000"><tt>libfact.so</tt></span>, cada uma em seu directório (<tt><span style="color: #990000">recurs/libfact.so</span></tt> e <tt><span style="color: #990000">iter/libfact.so</span></tt>). A selecção da variante a utilizar faz-se definindo a variável de ambiente <tt><span style="color: #990000">LD_LIBRARY_PATH</span></tt> com o directório apropriado. Indique quais os ficheiros iniciais modificados, face à alÃnea anterior, a nova <tt><span style="color: #990000">Makefile</span></tt> e os comandos CVS necessários para que o repositório passe a conter a nova versão.
| |
| # Modifique a alÃnea anterior para que o utilizador possa escolher a variante a utilizar através de um argumento na linha do comando <tt><span style="color: #990000">fact</span></tt>, respectivamente <tt><span style="color: #990000">recurs</span></tt> ou <tt><span style="color: #990000">iter</span></tt>. Indique quais os ficheiros iniciais modificados, a nova <tt><span style="color: #990000">Makefile</span></tt> e os comandos CVS necessários para registar a nova versão.
| |
| | |
| == Implementation ==
| |
| The following sections present possible implementations.
| |
| | |
| All shell commands are prefixed with <tt>prompt%</tt> (their output is presented for explanation purposes only and is not required to answer the problem).
| |
| | |
| It is assumed that the <tt>CVSROOT</tt> variable has been defined:
| |
| <bash>
| |
| export CVSROOT=/cvs
| |
| </bash>
| |
| | |
| === Step 1: Building the Project ===
| |
| | |
| Assuming that all files are in directory <tt>/some/temporary/directory</tt>, the following commands may be used to create the '''factorial''' project ().
| |
| | |
| prompt% cd /some/temporary/directory
| |
| prompt% cvs import factorial david initial
| |
| N factorial/recurs.cpp
| |
| N factorial/recurs.h
| |
| N factorial/iter.cpp
| |
| N factorial/iter.h
| |
| N factorial/main.cpp
| |
| | |
| Then, after import is complete, we can check-out a fresh copy of the project and change to that directory:
| |
| | |
| prompt% cvs co factorial
| |
| U factorial/iter.cpp
| |
| U factorial/iter.h
| |
| U factorial/main.cpp
| |
| U factorial/recurs.cpp
| |
| U factorial/recurs.h
| |
| prompt% cd factorial
| |
| | |
| === Step 2: Building the Makefile ===
| |
| | |
| The following is a simple Makefile for building the executable.
| |
| <text>
| |
| fact: main.o iter.o recurs.o
| |
| | |
| recurs.o: recurs.cpp
| |
| g++ -c recurs.cpp
| |
| | |
| iter.o: iter.cpp
| |
| g++ -c iter.cpp
| |
| | |
| main.o: main.cpp iter.h recurs.h
| |
| g++ -c main.cpp
| |
| </text>
| |
| | |
| The following is a slightly more complex Makefile for doing exactly the same thing. The possible advanytage of using this version is that it automates a few error-prone tasks (such as keeping dependencies up to date).
| |
| <text>
| |
| .PHONY: all depend
| |
| | |
| CXXFILES = $(wildcard *.cpp)
| |
| CXXHEADS = $(wildcard *.h)
| |
| OFILES = $(CXXFILES:%.cpp=%.o)
| |
| PROG = fact
| |
| | |
| %.o: %.cpp
| |
| $(CXX) $(CXXFLAGS) -c $< -o $@
| |
| | |
| all: depend $(PROG)
| |
| | |
| $(PROG): $(OFILES)
| |
| $(CXX) -o $@ $^
| |
| | |
| depend: .makedeps
| |
| | |
| .makedeps: $(CXXFILES) $(CXXHEADS)
| |
| $(CXX) $(CXXFLAGS) -MM $(CXXFILES) > .makedeps
| |
| | |
| -include .makedeps
| |
| </text>
| |
| | |
| <tt>.PHONY</tt> indicates targets that do not correspond to actual files and attempts should not be made to build them (e.g. from implicit rules). <tt>all</tt> depends on <tt>depend</tt> to force the Makefile to keep its dependencies updated without explicitly calling "make depend".
| |
| | |
| Finally, to put the Makefile under CVS control, the following two commands would be needed:
| |
| | |
| prompt% cvs add Makefile
| |
| cvs add: use `cvs commit' to add this file permanently
| |
| | |
| prompt% cvs commit
| |
| /cvs/factorial/Makefile,v <-- Makefile
| |
| initial revision: 1.1
| |
| | |
| === Step 3: The New Makefile ===
| |
| | |
| The following Makefile (a straightforward adaptation of the previous one) would solve the problem:
| |
| <text>
| |
| .PHONY: all depend
| |
| | |
| CXXFILES = $(wildcard *.cpp)
| |
| CXXHEADS = $(wildcard *.h)
| |
| ITER = iter
| |
| RECURS = recurs
| |
| | |
| %.o: %.cpp
| |
| $(CXX) $(CXXFLAGS) -c $< -o $@
| |
| | |
| all: depend $(ITER) $(RECURS)
| |
| | |
| $(ITER): main.o iter.o
| |
| $(CXX) -o $@ $^
| |
| | |
| $(RECURS): main.o recurs.o
| |
| $(CXX) -o $@ $^
| |
| | |
| depend: .makedeps
| |
| | |
| .makedeps: $(CXXFILES) $(CXXHEADS)
| |
| $(CXX) $(CXXFLAGS) -MM $(CXXFILES) > .makedeps
| |
| | |
| -include .makedeps
| |
| </text>
| |
| | |
| Note that we are assuming that the appropriate changes have been made to the code in the C++ files to allow for a single interface (the function is now called simply "fact") and multiple implementations.
| |
| | |
| Regarding CVS, only updates and commits are needed at this stage (new versions of the files will be sent to the repository).
| |
| | |
| === Step 4: The New Project Organization ===
| |
| | |
| In this case, we will need to reorganize the project. Since CVS does not support changes in file names or locations we will have to remove them from the old location and add them from the new location.
| |
| | |
| prompt% mkdir iter recurs
| |
| prompt% mv iter.cpp iter.h iter
| |
| prompt% mv recurs.cpp recurs.h recurs
| |
| prompt% cvs remove iter.cpp iter.h recurs.cpp recurs.h
| |
| cvs remove: use `cvs commit' to remove these files permanently
| |
| prompt% cvs add iter recurs
| |
| Directory /cvs/factorial/iter added to the repository
| |
| Directory /cvs/factorial/recurs added to the repository
| |
| prompt% cvs add iter/iter.cpp iter/iter.h recurs/recurs.cpp recurs/recurs.h
| |
| cvs add: use `cvs commit' to add these files permanently
| |
|
| |
| After updating the main file and the Makefile, the project's status is as follows:
| |
| | |
| prompt% cvs update
| |
| M Makefile
| |
| R iter.cpp
| |
| R iter.h
| |
| M main.cpp
| |
| R recurs.cpp
| |
| R recurs.h
| |
| A iter/iter.cpp
| |
| A iter/iter.h
| |
| A recurs/recurs.cpp
| |
| A recurs/recurs.h
| |
| | |
| The contents of the Makefile are as follows (we link with the "iter" version, but this is actually irrelevant, since the choice will always be dependent on <tt>LD_LIBRARY_PATH</tt>. Note the use of position-independent code, so that dynamic libraries do not cause problems (the linker will refuse to create the libraries if the code in the <tt>.o</tt> files is not position independent):
| |
| <text>
| |
| .PHONY: all depend
| |
| | |
| CXXFLAGS = -fPIC # use position-independent code
| |
| CXXFILES = $(wildcard *.cpp) $(wildcard iter/*.cpp) $(wildcard recurs/*.cpp)
| |
| CXXHEADS = $(wildcard *.h) $(wildcard iter/*.h) $(wildcard recurs/*.h)
| |
| LIBITER = iter/libfact.so
| |
| LIBRECURS = recurs/libfact.so
| |
| PROG = fact
| |
| | |
| %.o: %.cpp
| |
| $(CXX) $(CXXFLAGS) -c $< -o $@
| |
| | |
| all: depend $(LIBITER) $(LIBRECURS) $(PROG)
| |
| | |
| $(PROG): main.o
| |
| $(CXX) -o $@ $^ -Liter -lfact
| |
| | |
| $(LIBITER): iter/iter.o
| |
| $(CXX) -shared -o $@ $^
| |
| | |
| $(LIBRECURS): recurs/recurs.o
| |
| $(CXX) -shared -o $@ $^
| |
| | |
| depend: .makedeps
| |
| | |
| .makedeps: $(CXXFILES) $(CXXHEADS)
| |
| $(CXX) $(CXXFLAGS) -MM $(CXXFILES) > .makedeps
| |
| | |
| -include .makedeps
| |
| </text>
| |
| | |
| Inpecting the produced executable (in a Linux machine), without specifying a value for <tt>LD_LIBRARY_PATH</tt> and specifying the two possibilities:
| |
| | |
| prompt% ldd fact
| |
| libfact.so => not found
| |
| libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00002b5a6869c000)
| |
| libm.so.6 => /lib64/libm.so.6 (0x00002b5a689a4000)
| |
| libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00002b5a68bf8000)
| |
| libc.so.6 => /lib64/libc.so.6 (0x00002b5a68e06000)
| |
| /lib64/ld-linux-x86-64.so.2 (0x00002b5a6847f000)
| |
| | |
| prompt% LD_LIBRARY_PATH=iter ldd fact
| |
| libfact.so => iter/libfact.so (0x00002b804d64e000)
| |
| libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00002b804d87e000)
| |
| libm.so.6 => /lib64/libm.so.6 (0x00002b804db86000)
| |
| libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00002b804ddd9000)
| |
| libc.so.6 => /lib64/libc.so.6 (0x00002b804dfe8000)
| |
| /lib64/ld-linux-x86-64.so.2 (0x00002b804d431000)
| |
| | |
| prompt% LD_LIBRARY_PATH=recurs ldd fact
| |
| libfact.so => recurs/libfact.so (0x00002b553e03e000)
| |
| libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00002b553e26e000)
| |
| libm.so.6 => /lib64/libm.so.6 (0x00002b553e576000)
| |
| libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00002b553e7c9000)
| |
| libc.so.6 => /lib64/libc.so.6 (0x00002b553e9d8000)
| |
| /lib64/ld-linux-x86-64.so.2 (0x00002b553de21000)
| |
| | |
| === Step 5: User Control on Dynamic Linking ===
| |
| | |
| In this case, the main file is not linked with either of the two libraries. These are, instead explicitly open by the user's code and the appropriate symbol is called.
| |
| | |
| Note that we could have left the choice to <tt>LD_LIBRARY_PATH</tt> instead of providing an argument to the main program.
| |
| | |
| This is the new <tt>main.cpp</tt> file (note the name of the symbol corresponding to the "fact" function name in C++). A better style would perhaps be to use the <tt>extern "C"</tt> declaration.
| |
| <cpp>
| |
| #include <iostream>
| |
| #include <dlfcn.h>
| |
| | |
| static void usage(const char *myname) {
| |
| std::cerr << "Usage: " << myname << " (iter|recurs)" << std::endl;
| |
| exit(1);
| |
| }
| |
| | |
| int main(int argc, char **argv) {
| |
| if (argc != 2) usage(argv[0]);
| |
| | |
| void *handle;
| |
| if (!strcmp(argv[1], "iter")) handle = dlopen("iter/libfact.so", RTLD_LAZY);
| |
| else if (!strcmp(argv[1], "recurs")) handle = dlopen("recurs/libfact.so", RTLD_LAZY);
| |
| else usage(argv[0]);
| |
| | |
| void *fun = dlsym(handle, "_Z4facti"); // this is "fact" in C++
| |
| | |
| // cast void pointer into the appropriate function pointer
| |
| ((int(*)(int))fun)(5); // call function for 5!
| |
| }
| |
| </cpp>
| |
| | |
| The Makefile is the following:
| |
| <text>
| |
| .PHONY: all depend
| |
| | |
| CXXFLAGS = -fPIC # use position independent code
| |
| CXXFILES = $(wildcard *.cpp) $(wildcard iter/*.cpp) $(wildcard recurs/*.cpp)
| |
| CXXHEADS = $(wildcard *.h) $(wildcard iter/*.h) $(wildcard recurs/*.h)
| |
| LIBITER = iter/libfact.so
| |
| LIBRECURS = recurs/libfact.so
| |
| PROG = fact
| |
| | |
| %.o: %.cpp
| |
| $(CXX) $(CXXFLAGS) -c $< -o $@
| |
| | |
| all: depend $(LIBITER) $(LIBRECURS) $(PROG)
| |
| | |
| $(PROG): main.o
| |
| $(CXX) -o $@ $^ -ldl
| |
| | |
| $(LIBITER): iter/iter.o
| |
| $(CXX) -shared -o $@ $^
| |
| | |
| $(LIBRECURS): recurs/recurs.o
| |
| $(CXX) -shared -o $@ $^
| |
| | |
| depend: .makedeps
| |
| | |
| .makedeps: $(CXXFILES) $(CXXHEADS)
| |
| $(CXX) $(CXXFLAGS) -MM $(CXXFILES) > .makedeps
| |
| | |
| -include .makedeps
| |
| </text>
| |
| Regarding CVS, only the Makefile and the main file had to be changed: all there is to do is updating and commiting the changes:
| |
| prompt% cvs update
| |
| M Makefile
| |
| M main.cpp
| |
| | |
| prompt% cvs commit
| |
| /cvs/factorial/Makefile,v <-- Makefile
| |
| new revision: 1.2; previous revision: 1.1
| |
| /cvs/factorial/main.cpp,v <-- main.cpp
| |
| new revision: 1.3; previous revision: 1.2
| |
| | |
| [[category:Ensino]]
| |