CS1010 Compilation Guide
1. Compile a standalone C program
Suppose we have a standalone C program teh.c that does not use any external libraries. We can compile the program using the command
ooiwt@pe118:~$ clang teh.c
This command should create an executable called a.out in the current directory, which you can then run with:
ooiwt@pe118:~$ ./a.out
2. Renaming executable file
The name a.out is an abbreviation for assembler output, a name that many compilers kept as the default output name since the 60s. We should, however, give our executable more descriptive name, by using the -o flag. (o is the mnemonic for output).
ooiwt@pe118:~$ clang teh.c -o teh
or
ooiwt@pe118:~$ clang -o teh teh.c
The command above would create an executable called teh.
Beware of the order
If you are not careful and run the following command instead:
ooiwt@pe118:~$ clang -o teh.c teh
clang would overwrite your code teh.c -- all your hard work will be gone!!
3. Warning for possible bugs.
The clang checks for syntax errors in your C files -- i.e., things that violate the C syntax rules. The compiler, however, is smart enough to identify possible bugs -- errors that will cause your program to behave incorrectly, even if the syntax follows C's rules. You can ask clang to warn you about this, using the -W flag (W is the mnemonic for warning -- note the capital W). The manual for clang lists different types of warnings that clang can warn you about. For simplicity, we will ask clang to warn us about everything, by enabling all warnings. The command to do so is:
ooiwt@pe118:~$ clang -Wall teh.c -o teh
For beginners, it is highly recommended that you always compile with -Wall flag.
4. Generating additional information for debugging.
In order to use the debugger lldb to trace through and debug your program, clang needs to generate additional information and store them in the executable file. We can instruct clang to generate them with the flag -g (g for generate).
ooiwt@pe118:~$ clang -Wall -g teh.c -o teh
It is recommended that you always compile with -g flags during development phase. If you need to measure the performance (e.g., how fast it runs) of your program or when you are releasing the program to the public, you can remove the -g flag and compile with the optimization flags (e.g., -O) instead.
5. Linking with standard library.
To link with a standard library, we use the -l flag to specify the name of the library to link. For instance, to link with the C standard math library (abbreviated m), you issue the command:
ooiwt@pe118:~$ clang -Wall -g teh.c -o teh -lm
6. Linking with 3rd party library
By default, clang looks for headers and libraries in the systems directories (/usr/include, /usr/lib, etc) and the current working directory.
If you use a third party library, you usually need to tell clang where to look for the corresponding headers and libraries. You can use the -I flag and the -L flag for these purposes. For instance, if you have a library installed under your home called citadel, and the file citadel.h can be found under ~/citadel/include and the file libcitadel.a can be found under ~/citadel/lib, to tell clang where to find these files, you can compile with:
ooiwt@pe118:~$ clang -Wall -g -I ~/citadel/include -L ~/citadel/lib teh.c -o teh -lm -lcitadel