Compiling with the CSAPP library
The csapp collection of useful auxilliary functions are declared in the file csapp.h and defined in the csapp.c file.
These functions include the utility functions for Unix file i/o, sockets, signals, threads and semaphores.
The threads (and semphores) functions require linking with libraries other than the standard C library.
The threads functions require the pthread library.
On some systems (not ctilinux1), the semaphores also require the rt (run time) library.
Example 1
Goal: Compile a program sample.c that includes "csapp.h"
Assumptions: csapp.h and csapp.c are in the same directory as sample.c
gcc -O2 -lpthread -o sample sample.c csapp.c
On systems that also need to explicitly use the run time library, the command would just add another -l option:
gcc -O2 -lpthread -lrt -o sample sample.c csapp.c
Example 2
Goal: Same as Example 1, but avoid recompiling csapp.c every time.
In Example 1, the file csapp.c is recompiled every time you compile sample.c or any program that uses the csapp lib even though csapp.c doesn't change.
So you could compile (but not link) csapp.c just once to get an object file csapp.o:
gcc -O2 -c csapp.c
Then to compile sample.c
gcc -O2 -lpthread -o sample sample.c csapp.o
Example 3
Goal: Same as Example 2, but avoid having to type so much.
To reduce the amount of typing required, we could create a make file. The make command looks for files named makefile or Makefile.
We want the make command to read the makefile and automatically create the executable file sample from the files it depends on: sample.c and csapp.o.
But csapp.o depends on csapp.c.
So the makefile can have 2 targets: sample and csapp.o.
For each target we need to provide the command(s) to create the target. Each command line should begin with a tab!
sample: sample.c csapp.o
gcc -O2 -lpthread -o sample sample.c csapp.o
csapp.o: csapp.c
gcc -O2 -c csapp.c
To build sample all we need to type is:
make
Example 4
Goal: Compile any one of a fixed set of files that uses the csapp library without having to type too much.
Now suppose we have 3 separate programs: sample1.c, sample2.c, and sample3.c that use the csapp library.
We could write a makefile that has a target and rule for each one:
sample1: sample1.c csapp.o
gcc -O2 -lpthread -o sample1 sample1.c csapp.o
sample2: sample2.c csapp.o
gcc -O2 -lpthread -o sample2 sample2.c csapp.o
sample3: sample3.c csapp.o
gcc -O2 -lpthread -o sample3 sample3.c csapp.o
csapp.o: csapp.c
gcc -O2 -c csapp.c
To compile, say sample2, just type:
make sample2
Example 5
Goal: Compile any file that uses the csapp library without having to modify the makefile.
Instead of having to write an entry for each of the 3 programs in Example 4, we can also write a "rule" in the makefile that handles all 3 cases (and even an named xxx.c that uses csapp if it is added later):
.c:
gcc -O2 -lpthread -o $* $< csapp.o
csapp.o: csapp.c
gcc -O2 -c csapp.c
With this makefile, we can now compile and link any one of the .c files that uses csapp. For example to compile and link sample2.c:
make sample2
If csapp.c has not yet been compiled, this make command will automatically execute two commands:
gcc -O2 -c csapp.c
gcc -O2 -lpthread -o sample2 sample2.c csapp.o
Now sample2 can be executed and csapp.c has been also been compiled to produce csapp.o for further use.
So if we now want to compile sample3, we again just type
make sample3
Since csapp.o exists and is "up to date", only one command will be executed (automatically):
gcc -O2 -lpthread -o sample3 sample3.c csapp.o
Example 6
Goal: Same as Example 5, but also using only one copy of csapp.h and csapp.c that are located in one fixed separate directory.
All the preceding examples assume the csapp.h and csapp.c files are in the same directory as the file that will use them.
There is no reason to keep making copies of these files if they are not changing.
So suppose these files are in the subdirectory, say cslib, of your login directory: ~/cslib. That is, suppose the paths to the two files csapp.h and csapp.c are:
~/cslib/csapp.h
~/cslib/csapp.c
In some other directory, say ~/examples/threads in your account you have files sample1.c, sample2.c, etc. that will use the csapp library.
There is no need to copy the csapp.h or csapp.c files to the ~/examples/threads directory.
Instead, create a make file (named makefile) in the ~/examples/threads directory:
.c:
cd ~/cslib; make csapp.o
gcc -O2 -I ~/cslib -lpthread -o $* $<
This makefile has 2 commands to make the target.
The first command (temporarily) changes to the cslib directory and makes the csapp.o. Note that if csapp.o already exists, it will not be recompiled.
The second command (gcc ...) has an -I ~/cslib option. This tells the compiler to look in the ~/cslib directory for include files (csapp.h). It will also look there for any missing object files (csapp.o).