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guides:software:make:start

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guides:software:make:start [2020/07/20 14:48] – [Specifying a Single Target in a Makefile] wikiadminguides:software:make:start [2024/07/25 15:01] (current) – external edit 127.0.0.1
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 Make is a build automation tool that is designed to automatically construct executable programs from source code. Make is a build automation tool that is designed to automatically construct executable programs from source code.
 +
 +Make simplifies the build process for projects at all levels.
  
 ===== Simple Use ===== ===== Simple Use =====
Line 169: Line 171:
 </code> </code>
  
 +In the example:
 +  - The user types //ls// to show the contents of the directory
 +  - The user types //cat Makefile// to show the contents of the Makefile
 +  - The user types //make// to build the default target //hello//
 +  - The user types //ls// to show that hello was constructed
 +  - The user types //make clean// to remove project executable files.
 +  - The user types //ls// to show that the executable files have been removed.
 +
 +The Makefile contains the following:
 <code make> <code make>
 CXXFLAGS = -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion CXXFLAGS = -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion
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         rm -f hello         rm -f hello
 </code> </code>
 +
 +Note that an additional target, //clean//, has been added to the Makefile.  This target is different from the default target for all in two ways:
 +  - There are no dependencies
 +  - There is a //rule// to be applied when building the target.
 +
 +The rule is //rm -f hello//.  This is a shell command that will be executed when make attempts to build the target.  In this case, the result is to remove the file //hello//.  The //-f// flag says to force the removal of the file, but in this case the purpose is to make //rm// ignore non-existent files.  This keeps make from reporting an error if hello is not present.
 +
 +Note that when constructing rules in make, the rules need to be indented by a tab.  The following example demonstrates what would happen if //rm -f hello// were not preceded by a tab.
 +
 +<code>
 +$ cat Makefile
 +CXXFLAGS = -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion
 +
 +all: hello
 +
 +clean:
 + rm -f hello
 +$ make
 +Makefile:6: *** missing separator.  Stop.
 +</code>
 +
 +In this example:
 +  - The user types //cat Makefile// to show the contents of the Makefile
 +    - Notice that the rule for //clean// has a space and not a tab.
 +  - The user types //make// to build the project
 +    - Make reports an error because it can not parse the Makefile due to the missing tab.
 +
 +It is extremely important that all rules for a target begin with a tab.
 +
 +===== Building Multiple Targets =====
 +
 +<code>
 +$ ls
 +Makefile  greeting.cpp  hello.cpp  salute.cpp
 +$ cat Makefile
 +CXXFLAGS = -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion
 +
 +OBJS = hello greeting salute
 +
 +all: ${OBJS}
 +
 +clean:
 +        rm -f ${OBJS}
 +$ make
 +g++ -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion    hello.cpp   -o hello
 +g++ -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion    greeting.cpp   -o greeting
 +g++ -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion    salute.cpp   -o salute
 +$ ls
 +Makefile  greeting*  greeting.cpp  hello*  hello.cpp  salute*  salute.cpp
 +$ make clean
 +rm -f hello greeting salute
 +$ ls
 +Makefile  greeting.cpp  hello.cpp  salute.cpp
 +</code>
 +
 +In this example:
 +  - The user types //ls// to show the contents of the directory
 +    - Note that three independent source code files exist //greeting.cpp, hello.cpp, and salute.cpp//.
 +  - The user types //cat Makefile// to show the contents of the makefile.
 +    - The changes will be explained below.
 +  - The user types //make// to build all primary targets.
 +    - Make constructs three executables, //hello, greeting//, and //salute//.
 +  - The user types //ls// to show the contents of the directory after the build.
 +  - The user types //make clean// to clean up the project directory
 +    - Make removes all of the executable files produced in the previous step.
 +  - The user types //ls// to show the contents of the directory.
 +
 +The makefile has been modified on three lines.
 +
 +First, a variable called //OBJS// has been added.  This contains the name of all of the programs that should become part of the default target.  By declaring this variable, more programs can be added to the default target by adding their name to the value of this variable.
 +
 +<code make>
 +OBJS = hello greeting salute
 +</code>
 +
 +Secondly, the default target has been changed.  Instead of listing a single target, or even multiple targets, the variable //OBJS// is specified.  Make will replace this variable with the values stored in the variable.  The variable is specified as //${OBJS}// in this case.    Don't worry about the syntax, just copy it.  As you learn more about //shell programming// this syntax will be easier to understand.
 +
 +<code make>
 +all: ${OBJS}
 +</code>
 +
 +Finally, the rule to make clean has been altered to remove all of the files listed in the variable //OBJS//.
 +
 +<code make>
 +clean:
 +        rm -f ${OBJS}
 +</code>
 +
 +The final makefile for this section is:
 +<code make>
 +CXXFLAGS = -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion
 +
 +OBJS = hello greeting salute
 +
 +all: ${OBJS}
 +
 +clean:
 +        rm -f ${OBJS}
 +</code>
 +
  
  
 ===== Makefiles for Multiple File Compilation ===== ===== Makefiles for Multiple File Compilation =====
 +
 +One of the most powerful uses of make is to compile multiple files into a single executable.
 +
 +==== Example ====
 +
 +For this example the code is decomposed into the following files:
 +
 +  * //stringTools.h// defines a method for converting a string to lowercase
 +    * <code c++>
 +#ifndef STRING_TOOLS
 +#define STRING_TOOLS
 +
 +void  LowerCase(std::string & word);
 +
 +#endif
 +</code>
 +  * //stringTools.cpp// implements the code in stringTools.h
 +    * <code c++>
 +include <iostream>
 +#include <cstdlib> // gives access to tolower
 +#include "stringTools.h"
 +
 +using namespace std;
 +
 +void  LowerCase(string & word){
 +    for(auto &x : word) {
 +       x = static_cast<char> (tolower(static_cast<int> (x)));
 +    }
 +
 +    return;
 +}
 +</code>
 +
 +  * //greeting.h//
 +    * <code c++>
 +#ifndef GREETING
 +#define GREETING
 +
 +std::string GreetingString(std::string language);
 +
 +#endif
 +</code>
 +  * //greeting.cpp//
 +    * <code c++>
 +
 +#include <iostream>
 +
 +#include "greeting.h"
 +#include "stringTools.h"
 +
 +using namespace std;
 +
 +string GreetingString(string language){
 +    string greeting = "Hello World";
 +
 +    LowerCase(language);
 +
 +    if (language == "pig") {
 +       greeting = "Ellohay Orldway";
 +    } else if (language == "ubbi") {
 +       greeting = "Hubellubo Wuborublubdub";
 +    }
 +
 +    return greeting;
 +}
 +</code>
 +  * //hello.cpp//
 +    * <code c++>
 +#include <iostream>
 +
 +#include "greeting.h"
 +
 +using namespace std;
 +
 +int main() {
 +    string languages[] = {"PIG", "piG","UBBI", ""};
 +
 +    for (auto lang: languages) {
 +        cout << " The greeting in \"" << lang << "\"" << endl;
 +        cout << GreetingString(lang) << "!" << endl;
 +    }
 +
 +    return 0;
 +}
 +</code>
 +  * //Makefile//
 +    * <code make>
 +CXXFLAGS = -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wu
 +ninitialized -Wshadow -Wconversion -std=c++14
 +
 +OBJS =  hello
 +
 +all: ${OBJS}
 +
 +hello: greeting.o stringTools.o
 +
 +greeting.o: greeting.h stringTools.h
 +
 +stringTools.o: stringTools.h
 +
 +clean:
 +        rm -f ${OBJS} *.o
 +</code>
 +
 +To build this code, you are required to compile stringTools.cpp into stringTools.o, greeting.cpp into greeting.o and finally build hello from hello.cpp, stringTools.o and greeting.o.
 +
 +This could be accomplished by hand by executing the following
 +<code>
 +g++ -c greeting.cpp
 +g++ -c stringTools.cpp
 +g++ -o hello hello.cpp stringTools.o greeting.o
 +</code>
 +
 +Of course, if you have command line flags, this becomes much more complex.  In addition, you need to remember to recompile ALL of the proper files when any of the files change, this includes the header files.  Using make simplifies this process.
 +
 +Using the above //Makefile// the code can be built with one command 
 +
 +<code> 
 +$ make
 +g++ -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion -std=c++14   -c -o greeting.o greeting.cpp
 +g++ -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion -std=c++14   -c -o stringTools.o stringTools.cpp
 +g++ -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion -std=c++14    hello.cpp greeting.o stringTools.o   -o hello
 +$ ls
 +Makefile      greeting.h  hello*     stringTools.cpp  stringTools.o
 +greeting.cpp  greeting.o  hello.cpp  stringTools.h
 +</code>
 +
 +Note that all components are compiled and the final executable is produced.  If any of the component files change, make will recompile only the parts necessary to rebuild the entire project.  For example, if greeting.cpp were change, that file, along with hello.cpp would need to be recomipled, but stringTools.o would not need to be rebuilt.
 +
 +<code>
 +$ touch greeting.cpp
 +$ make
 +g++ -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion -std=c++14   -c -o greeting.o greeting.cpp
 +g++ -g -O3 -Wpedantic -Wall -Wextra -Wmisleading-indentation -Wunused -Wuninitialized -Wshadow -Wconversion -std=c++14    hello.cpp greeting.o stringTools.o   -o hello
 +</code>
 +
 +==== The Makefile ====
 +
 +In order to build this project using make, you need to inform make of the dependencies built into the project.  In this case, to build hello, we need to have both //greeting.o// and //stringTools.o// because the code in hello calls code in both of these files.  The following line in the makefile performs this task
 +
 +<code make>
 +hello:  greeting.o stringTools.o
 +</code>
 +
 +You do not need to tell make that //hello// depends on //hello.cpp//, that is built into the system.
 +
 +You also do not need to tell make that //hello// depends on //greeting.h// or //stringTools.h//.  This is accomplished by the next set of instructions in the makefile.
 +
 +<code make>
 +stringTools.o: stringTools.h
 +</code> 
 +
 +This line tells make that //stringTools.o// depends on //stringTools.h//.  Make does not have default rules for header files, so this line is necessary.  The result of this line is if stringTools.h changes, stringTools.o will need to be rebuilt.   If this happens, make is able to deduce that //hello// will need to be rebuilt as well.  This is good since //hello.cpp// includes //stringTools.h//.
 +
 +<code make>
 +greeting.o: greeting.h stringTools.h
 +</code>
 +
 +This line tells make that //greeting.o// depends on both //greeting.h// and //stringTools.h//.  Again //greeting.o// also depends on //greeting.cpp//, but make has this rule built in.  
  
guides/software/make/start.1595256526.txt.gz · Last modified: 2024/07/25 15:01 (external edit)