Simple Makefile Including Compilation of Shared Object Library

This post covers two main concepts: a simple Makefile generation and compiling a shared object library within this Makefile.
Directory structure is designed as this:

• ../MakeFileProj (MakeFile)
• ../MakeFileProj/inc (Headers: test1.h, test2.h)
• ../MakeFileProj/src (Source Files: main.c test1.c test2.c)
• ../MakeFileProj/obj (Object Files: main.o test1.o test2.o)
• ../MakeFileProj/lib (Library Files: libtest2.so -> test2.c is compiled as shared object library)

The source and header files are given below:

	/*test1.h*/
	#ifndef test1_h__
	#define test1_h__
	void test1Message(void);
	#endif

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	/*test1.c*/
	#include <stdio.h>
	#include "../inc/test1.h"
	void test1Message(void){
	printf("\nsZr test1Message: This is not a shared library");
	}

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	/*test2.h*/
	#ifndef test2_h__
	#define test2_h__
	void test2Message(void);
	#endif

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	/*test2.c*/
	#include <stdio.h>
	#include "../inc/test2.h"
	void test2Message(void){
	printf("\nsZr test2Message: This is a SHARED LIBRARY");
	}

view raw gistfile1.c hosted with ❤ by GitHub

	/*main.c*/
	#include <stdio.h>
	#include "../inc/test1.h"
	#include "../inc/test2.h"
	int main(int argc, char const *argv[])
	{
	/* code */
	printf("\nsZr Welcome to MakeFileProject...");
	test1Message();
	test2Message();
	return 0;
	}

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Makefile is as shown below:
As source, test1.c and main.c are compiled and object files are created under /obj directory. However test2.c is compiled as a shared object library and the .so file created under /lib. Finally, the object files and the .so library are linked to create "test" executable.

	#MakeFile
	#Author: Sezerb
	#Compiles test1.c, main.c as source code.
	#Compiles test2.c as a shared object lib.
	#Creates test as an executable.
	#Current Working Directory
	CWD=$(shell pwd)
	#define C compiler
	CC = gcc
	#define Compiler Flags
	CFLAGS = -g -Wall
	#define Path of Header Files
	INCLUDE = $(CWD)/inc
	INCLUDES = -I$(INCLUDE)
	#define library paths and Linker flags
	LFLAGS = -L$(CWD)/lib
	LDFLAGS = -shared
	#define libraries to link
	LIBS = -ltest2
	#define Source Files and Object Files
	SRC = $(CWD)/src
	SRCS = $(SRC)/main.c $(SRC)/test1.c
	OBJ = $(CWD)/obj
	OBJS = $(OBJ)/main.o $(OBJ)/test1.o
	#define Library Source Files
	LIB_SRC = $(CWD)/src
	LIB_SRCS = $(SRC)/test2.c
	LIBS = -ltest2
	#define name of executable
	MAIN = test
	all: $(MAIN)
	$(MAIN): main.o test1.o libtest2.so
	@echo test has been compiled...
	$(CC) $(CFLAGS) $(INCLUDES) -o $(MAIN) $(OBJS) $(LFLAGS) $(LIBS)
	main.o: $(SRC)/main.c $(INCLUDE)
	$(CC) $(CFLAGS) -c $(SRC)/main.c -o $(OBJ)/main.o
	@echo main.o is created...
	test1.o: $(SRC)/test1.c $(INCLUDE)
	$(CC) $(CFLAGS) -c $(SRC)/test1.c -o $(OBJ)/test1.o
	@echo test1.o is created...
	libtest2.so: $(LIB_SRCS) $(INCLUDE)
	$(CC) $(CFLAGS) -c $(LIB_SRCS) -o $(OBJ)/test2.o
	$(CC) $(LDFLAGS) -o $(CWD)/lib/libtest2.so $(OBJ)/test2.o
	@echo libtest2.so shared object is created...
	.PHONY: clean
	clean:
	$(RM) main $(MAIN) *~ $(CWD)/lib/*.* $(OBJ)/*.*

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After compilation succesfully one can try the executable file in console as:
$ ./test
$ ./test: error while loading shared libraries: libtest2.so: cannot open shared object file: No such file or directory
At run-time the executable file cannot find shared object library, so we should add it to LD_LIBRARY_PATH.
$ export LD_LIBRARY_PATH=/home/sezerb/Desktop/MakeFileProj/lib:$LD_LIBRARY_PATH
Do not forget to use your own path, where libtest2.so is located. Then try ./test again:
$ ./test
$ sZr Welcome to MakeFileProject...
$ sZr test1Message: This is not a shared library
$ sZr test2Message: This is a SHARED LIBRARY

This Makefile should be a reference one for our projects...
Take care yourselves!..