This repository is the workshop materials for the Linux@App Introduction to C event.

This repository is intended to teach the following skills:

• Basic C compiler usage
• Basic C preprocessor tricks
• Basic C types
• Basic functions
• C strings and memory management
• Basic structures
• How to get help with and use the C standard library

You need a UNIX machine with gcc, git, make, and some kind of text editor. You should know how to run programs in a terminal. Basic programming experience in another language is also important.

This repository contains a series of makefiles that operate on different files to automate compilation. Use these as a reference to learn the various flags that the gcc command accepts.

Acquire a copy of the files:

git clone https://github.com/whereswaldon/intro2c.git

First, cd into the first directory and run make first-all. The outputs that are generated are the results from each stage of the c compilation pipeline:

• first.E is the result of running the preprocessor. You should look at this, as it will help make sense of what #include actually does
• first.s is the compiled version of the code. It is presented in human-readable assembly language.
• first.o is the assembled version of the code. It is a binary file, so view it with xxd or similar. Ordinarily, several object files are combined to form an executable, which is the stage after assembling in the compilation pipeline.
• first is an executable file built by linking first.o. Try it with ./first.

Go into the cond directory and look at cond.c. This file demonstrates how you can implement conditional logic with the preprocessor. If the symbol YES is defined when it is compiled, it will print one thing. Otherwise, it will print another.

Try:

$ gcc -DYES=1 -o cond cond.c
$ ./cond

Then, try:

$ gcc -o cond cond.c
$ ./cond

The output is different because the preprocessor literally rewrote the code depending on whether the symbol YES was defined. As you can see, the -D flag to the compiler lets us define a preprocessor symbol on the compiler command line.

We can also define symbols in our code with:

#define YES 1

Note that we are not assigning with a = symbol. The symbol name and value are separated by a space.

Go into the types directory and look at types.c in a code editor (syntax highlighting will be nice). Read through it and try the challenges.

Go into the funcs directory and look at funcs.c in a code editor. Read through it and try the challenge.

Go into the str_mem directory and look at str_mem.c in a code editor. Read through it and try the challenge.

Go into the struct directory and look at struct.c in a code editor. Read through it and try the challenge.

Most languages have a source of documentation that we consult on the internet, but doing that for C can be quite frustrating. The documentation is out there, but it can be hard to find. This is because most C programmers don't need to go to the internet to find it. Linux systems actually already have all of the documentation for the C standard library. You just need to know how to find it.

If you want to get help with a subject like strings, try the following:

$ apropos string | less

The apropos command searches the installed documentation for information relevant to the keywords that you provided.

<output truncated>
stpcpy (3)           - copy a string returning a pointer to its end
stpncpy (3)          - copy a fixed-size string, returning a pointer to its end
strcasecmp (3)       - compare two strings ignoring case
strcasestr (3)       - locate a substring
strcat (3)           - concatenate two strings
strchr (3)           - locate character in string
strchrnul (3)        - locate character in string
strcmp (3)           - compare two strings
strcoll (3)          - compare two strings using the current locale
strcpy (3)           - copy a string
<output truncated>

Each line of output is a documentation page related to your keyword. To view that documentation, you can type:

man <paren-num> <first-word>

So to view strcmp (3) ..., I would type man 3 strcmp.