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C Basics

Some basic concepts about the programming language C

2023-09-19

Tips

Use void in functions without parameters. For example: int main(void) { ... }
Use #pragma once at the beginning of a header file to prevent multiple inclusion.
Use the compiler flags -Wall and -Wextra for additional hints.

Error Handling

The different ways to handle errors in C

Use a custom shared library

The shared library gets linked during runtime. A shared library should start with the prefix lib.

Copy the header file to /usr/local/include/.
Compile the shared library with cc -o libtest -shared -fPIC libtest.c.
Copy the shared library to /usr/local/lib/.
Add the folder to /etc/ld.so.conf if the entry doesn't already exist.
Run ldconfig to load the library. Check with ldconfig -p | grep libterm if the library was loaded correctly.
Include the library with #include <libtest.h>.
Compile your application with cc -o main -ltest main.c. Run ldd main to see if the library is listed as dependency.

The following Makefile show how to create simple install/uninstall options:

Makefile

%gdefault:%n build

%gbuild:%n
  cc -o libtest -shared -fPIC libtest.c

%ginstall:%n build
  sudo cp libtest.h /usr/local/include/
  sudo cp libtest.so /usr/local/lib/
  sudo ldconfig
  rm libtest.so

%guninstall:%n
  sudo rm /usr/local/include/libtest.h
  sudo rm /usr/local/lib/libtest.so

%gclean:%n
  rm libtest.so

Libraries

curl
libpq-fe
openssl
cmark
toml

Tools

Command	Description
`man <topic>`	View manual for a specific topic
`xxd <file>`	View binary file as hex
`ldd <file>`	View binary dependencies
`file <file>`	View file type