CS201

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CS201 Makefile

• Tutorial

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A Trivial Makefile
Trivial Makefile for puzzle1.c Ray S.
Babcock, CS201, MSU-Bozeman 1/5/05 puzzle1
puzzle1.c gcc o puzzle1 puzzle1.c
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A Trivial Makefile
Trivial Makefile for puzzle1.c Ray S.
Babcock, CS201, MSU-Bozeman 1/5/05 puzzle1
puzzle1.c gcc o puzzle1 puzzle1.c
COMMENTS
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A Trivial Makefile
Trivial Makefile for puzzle1.c Ray S.
Babcock, CS201, MSU-Bozeman 1/5/05 puzzle1
puzzle1.c gcc o puzzle1 puzzle1.c
Target
Targets Prerequisites
Dependency Line
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Whats happening here?
Source File
puzzle1.c
Gnu C compiler
gcc
Run Image
Depends on
puzzle1
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So whats a run image file?

• A run image file is an exact copy of the
  computers ram memory containing the binary
  equivalent of the program.
• To run the program, you load the run image file
  and point your computer to the start of the
  program. This is done by typing the run image
  file name at the operating system prompt.
• puzzle1

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A Trivial Makefile
Trivial Makefile for puzzle1.c Ray S.
Babcock, CS201, MSU-Bozeman 1/5/05 puzzle1
puzzle1.c gcc o puzzle1 puzzle1.c
Time stamp on this file
is compared to the time stamp on this file.
Dependency Line
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A Trivial Makefile
Trivial Makefile for puzzle1.c Ray S.
Babcock, CS201, MSU-Bozeman 1/5/05 puzzle1
puzzle1.c gcc o puzzle1 puzzle1.c
Time stamp on this file
is compared to the time stamp on this file.
Dependency Line
If the targets time stamp is earlier than the
prerequisites time stamp, the rule below this
dependency line is executed.
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So what is a time stamp?

• The time that the file was last modified.
• If the targets time is earlier than the
  prerequisites time, this means that the
  prerequisite file has been changed, but the run
  image has not been updated.

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A Trivial Makefile
Trivial Makefile for puzzle1.c Ray S.
Babcock, CS201, MSU-Bozeman 1/5/05 puzzle1
puzzle1.c gcc o puzzle1 puzzle1.c
Rule Line
Must be a tab!!
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A Trivial Makefile
Trivial Makefile for puzzle1.c Ray S.
Babcock, CS201, MSU-Bozeman 1/5/05 puzzle1
puzzle1.c gcc o puzzle1 puzzle1.c
Rule Line
Any Linux command
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Example time stamps

• Assume puzzle1 has TS Jan 16 1400
• Assume puzzle1.c has TS Jan 16 1355
• Target is LATER than prerequisite, so rule is NOT
  executed!

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Example time stamps

• Assume puzzle1 has TS Jan 16 1300
• Assume puzzle1.c has TS Jan 16 1355
• Target is EARLIER than prerequisite, so rule is
  executed!

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Example

• Build a source file with code for puzzle1.c
• Build a Makefile with an appropriate dependency
  line.
• Run make
• make
• gcc -o puzzle1 puzzle1.c
• The rule executes since the file puzzle1 does not
  even exist yet!

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What if you tried make again?

• make
• make puzzle1 is up to date

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Makefile Summary

• Build a dependency line for every target.
• Add a rule line to rebuild the target.
• Start the rule line with a tab.
• Add comments to the top of the file.
• Save these lines in an ASCII file called
  Makefile. (For now assume it must be exactly
  that name, with a capital M).