Software Development: Multiple File Development + Makefile

Motivation
- organization of modules
  - cut problem and abstraction
  - information hiding
- software module re-use
- programming team logistics
  - multiple developers
  - distinct locations
Typical case
- each module in separate source file
- include head file for a function in other source file
Steps in software build
- Linker
  - merges together independently-complied object code modules
  - resolve external reference among modules
  - typically loading
  - output
    - executable file
    - dynamically loading libraries
    - other
Makefiles
- make command control file defaults to makefile
- target
  - objects(files) that must be brought up-to-date
- dependency
  - list of target influence the main target
- action
  - command that are executed if any of the dependency objects has a time-stamp more recent than the target
- rule
  - specification of target, dependency and action.
- makefile format
  - make [-f makfile] [option] [target0…..](use makefile in make command)
    - all target and makefile must located in current working directory
  - Phony rules
    - .PHONY tell make that the rule doesn`t generate a file with the target name
- Macros
  - observation: compiler opitions keep having to be repeated all over the place
    - tedious
    - error-prone
    - difficult to maintain
  - use Macros
    - variableName = text
    - use $variableName in makefile
    - pre-defined Marcos
      - CC
        
        C compiler to use
      - CXX
        
        C++ compiler to use
      - CFLAGS
        
        Flags to C compiler
      - CXXFLAGS
        
        Flags to C++ compiler
      - LDFLAGS
        
        Flag to Linker (ld)
      - …
    - can used in avoid retyping filename in makefile
- Implicit rules
  - make have predefined rules for “standard dependency” for generate .o file from .cc and .c file
  - use suffixes(后缀) of file to infer what command to perform
  - use of pre-defined Macros
- Features
  - automatic generate dependency
  - conditionals(if / else between file)
  - all environment variable available with same name
  - automatic generate makefile
    - cmake
    - automake
- Options
  - -n: Don’t actually run any recipe; just print them.
  - -W file: pretend target file is just modified
  - -trace: Print tracing information.