Compiling Code and Make Introduction.

Objectives

1. Understand how to use make
2. Understand how to create a Makefile
3. Understand some compiler flags and how they can help us avoid errors.

Notes

• Sorry, this is from my knowledge.
• We have seen some of this.
  • If we have the file example.cpp
  • g++ example.cpp
    • Will produce the executable file a.out
    • But this is the name of all files compiled
    • And we have no idea where the executable came from.
  • g++ -o example example.cpp
    • Will produce the executable file example
  • make example will do the same thing.
  • If we create a file called Makefile

    • all: example 

    • We can then just type make to compile our executable.
• -o example is an example of a compiler option or in general a command line argument.
  • There are a lot of these.
  • They control
    • The language used
      • --std=c++14, --std=c++17, --std==c++2a
    • Optimization and debugging
      • -g, -O1, -O2, ...
    • Error/convention checking
      • -Wall -Wextra -Werror
• For now, you need to use the following compiler flags:

   -g -O2  -Wall -Wextra -Werror 

• Let's experiment with some of them.
  • g++ -Wuninitalized uninit.cpp -o uninit
    • What are warnings?
      • Issued by the compiler
      • Statements that the syntactically legal code probably has other errors.
      • Look at uninit.cpp.
    • In this case, it is legal to declare and use an uninitialized variable, but you should not.
    • -Wall and -Wextra
      • Check for many common mistakes like this.
      • And we should take advantage of this.
      • g++ -Wall -Wextra badLoop.cpp -o badLoop
    • To be graded, your code must compile without warnings, including those caused by -Wall -Wextra
  • -Werror turns all warnings into errors.
    • WHy?
    • g++ -Wall -Wextra -Werror badLoop.cpp -o badLoop
• A Makefile template

  # add the names of the programs you want to compile here
  OBJS = 
  CXXFLAGS =  -g -O2 -Wall -Wextra -Werror
  
  all: ${OBJS}
  
  # the rm line starts with a tab.
  clean:
      rm -f ${OBJS} *.o 

  • Add the names of the programs you want to compile to the OBJS line

    • OBJS = uninit badParam

    • When you type make, this will build the executables uninit and badParam
  • The last line rm -f *.o ${OBJS}
    • MUST START WITH A TAB
    • No spaces after the *
• Here is a Makefile.
  • make will build any executables listed in OBJS
  • make clean will remove the executables and any .o files.
  • make -n will show what will happen.
  • make anything will build anything with the flags specified in the Makefile
• We will add to this later.