Makefile

A makefile is a file (by default named 'Makefile') containing a set of directives used by a make build automation tool to generate a target/goal. A makefile is a file (by default named 'Makefile') containing a set of directives used by a make build automation tool to generate a target/goal. Most often, the makefile directs Make on how to compile and link a program. A makefile works upon the principle that files only need recreating if their dependencies are newer than the file being created/recreated. The makefile is recursively carried out (with dependency prepared before each target depending upon them) until everything has been updated (that requires updating) and the primary/ultimate target is complete. These instructions with their dependencies are specified in a makefile. If none of the files that are prerequisites have been changed since the last time the program was compiled, no actions take place. For large software projects, using Makefiles can substantially reduce build times if only a few source files have changed. Using C/C++ as an example, when a C/C++ source file is changed, it must be recompiled. If a header file has changed, each C/C++ source file that includes the header file must be recompiled to be safe. Each compilation produces an object file corresponding to the source file. Finally, if any source file has been recompiled, all the object files, whether newly made or saved from previous compilations, must be linked together to produce the new executable program. Makefiles originated on Unix-like systems and are still a primary software build mechanism in such environments. Windows supports a variation of makefiles with its nmake utility. Standard Unix-like makefiles can be executed in Windows in a Cygwin environment or Mingw. Makefiles contain five kinds of things: explicit rules, implicit rules, variable definitions, directives, and comments.