make_tutorial

Based on https://www.udemy.com/course/make-and-makefile-for-cc-projects-2022-edition/ and
https://github.com/franneck94/UdemyMakefile

Compilation steps

Usually, to build the project binary, it involves preprocessing,
generation of object files against each source file and finally
linking the libs and all the generated objects, to generate
executable binary.

Compilation

• To produce object file main.o
  
• command:
  g++ main.cpp -c

Compiler Flags

• Debug: -g, includes the following in the exec binary:

  • debug information: help debugging tools to enable debug.
  • Symbol Tables: names, types of var, functions, symbols.
  • Line numbers: map breakpoints to specific line in src.
  • Function names.

• Release: -O0 -O1 -O2 -O3 -Og -Os

  • -O0: No optimization, for debugging.
  • -O1: Basic performance optimization.
  • -O2: Higher performance optimization.
  • -O3: Advanced performance optimization.
  • -Os: Optimize for smaller code size.
  • -Og: Optimize for debugging.

• Includes: -I

  • Include directory path for header files

• Warnings: -Wall -Wextra -Wpedantic -Wconversion

  • -Wall: Enable most warnings.
  • -Wextra: Enable extra warnings.
  • -Wpedantic: Enforce strict standards.
  • -Wconversion: Warn about type conversions.

Linker

• Link object files, generate exec/binary.
• command: g++ main.o -o main.
• -L: flag to indicate path to libraries.
• -l: flag to pass a library to link. Example: -lpthread.
• -T: linker script linker_script.ld file.

About Makefile

Makefile basics

• In a Makefile, we have
  • targets and
  • dependencies.
• Generally, targets are expected to be files.
• so it is make file, but they can also be just names.
• Dependecies can be other targets or files. To run make:

    $ make target (a.k.a file)

• Inside a makefile, we have:

    target: depedency1 depedency2
        command1
        command2

• The tab after the target line is important for make to parse the Makefile.
• % is wildcard operator, for more details, refer 04_variables.

.PHONY

When a target is not to be associated with a file (name), and we declare the target as .PHONY. For example, in our project we have target build and we have build folder. Without .PHONY, running make build would results in "upto date", as there is no change on build folder. To just run it as target and not associate it with this folder, declare it as .PHONY .

• Use .PHONY in a Makefile to declare a target that must not related to a file.
• Example: You have a "build" target and a "build" folder in your project.
• Without .PHONY, running make build may result in "up to date", i.e., no build, because the folder as a file doesn't change.
• To run it as a target only, without associating it to the folder (file), declare it as .PHONY.

    .PHONY: build clean

Fetching Target, dependencies in Target command statements

• Let us go with an example:

    build_target: dependecy1 dependecy2 depdency3

• $@: gives the name of the target, i.e.,"build_target".
• $<: gives the name of the first dependency, i.e.,"dependecy1".
• $^: gives the name of all dependencies, i.e.,"dependecy1 dependecy2 depdency3".

Makefile variables

VARIABLE_NAME = Value

• Value is always a string.
• They can be referred by $(VARIABLE_NAME) in makefile.
• To get global pre-defined make variables, just run:

$ make -p

• They can be overidded by passing over at make command.

$ make VARIABLE_NAME=ValueA