Makefile to Compile OpenCV Code in C++ on Ubuntu/Linux - opencv

Question

I am learning OpenCV using Learning OpenCV book.
One problem I am facing while compiling the code is that I have to write a long command to compile and get the executable.
This is the command I am using
g++ `pkg-config –cflags opencv` file_name.cpp -o output_file `pkg-config –libs opencv`
I am no Make expert but I think I can eliminate writing that long command using make.
Before that I should explain my work flow. I have created a directory called opencv in my home directory (~/opencv/). I am reading the book section by section and coding the examples or exercises into new cpp source code files in that directory. So I don't know the names of the files before hand.
Now what I want make to do is,
Suppose I have coded a new file named facedetect.cpp in my opencv directory, and if I call make like this
make facedetect
then I want make to execute the following command for me
g++ `pkg-config --cflags opencv` facedetect.cpp -o facedetect `pkg-config --libs opencv`
so that whenever I make a new file named abc.cpp, I will execute make abc
so that I can run
$ ./abc
at my command line to test my abc.cpp
Please give that make file so that I can save the frustration of typing that long command each time.
PS: I have Googled for help on this and found this on using CMake but I could not understand what that does. Kindly also explain how can I use CMake for the same task.

Answer 1

You can create a file called Makefile in you working directory like this:
CFLAGS = `pkg-config --cflags opencv`
LIBS = `pkg-config --libs opencv`
% : %.cpp
g++ $(CFLAGS) $(LIBS) -o $# $<
then you can use this file for all your single-file programms. Just call make with the basename of the file you want to compile. For facedetect.cpp that would be
make facedetect
Here some more details:
The general format of a makefile is like this:
target : dependecy1 dependenc2 ...
command that generates the target
So for your example you could write:
facedetect : facedetect.cpp
g++ $(CFLAGS) $(LIBS) -o facedetect facedetect.cpp
For each new example you can now create a new target. But you can also make it more general:
% : %.cpp
g++ $(CFLAGS) $(LIBS) -o $# $<
Here % matches any nonempty substring. The automatic variables $# and $< substitute the names of the target file and the source file.
For more information you can consult the make documentation.

Answer 2

GNU Make is pretty smart and the Makefile you need for this doesn't need to be as verbose as in the other answers given so far. Here is a simple Makefile which you can use to compile the OpenCV examples:
CPPFLAGS = $(shell pkg-config --cflags opencv)
LDLIBS = $(shell pkg-config --libs opencv)
That's it. The Makefile can be this short thanks to Make's implicit rules.
Then run make as usual:
make facedetect
This assumes there is a facedetect.c or facedetect.cpp in the same directory.
I recommend the following (free!) book if you want to learn Make: http://oreilly.com/catalog/make3/book/index.csp

Answer 3

Create a file named makefile in your working directory that contains the following:
CFLAGS = $SHELL(pkg-config --cflags opencv)
LIBS = $SHELL(pkg-config --libs opencv)
facedetect : facedetect.cpp
g++ $(CFLAGS) $(LIBS) -o $# $<
Then when you want to compile you just type:
$ make
(To answer your PS - note that CMake is very different from make - for now you should probaby just use make.)