EECS 201 - Class 9: Libraries

# Overview
1. Announcements
2. Review
3. Q&A
4. Basic assignment
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# Announcements
* Python assignments due today
* Libraries assignments due June 19
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# Review
* Static libraries go directly inside the executable
  * Libraries are an inherent part of the executable
* Dynamic/shared libraries are referred to by the executable
  * Libraries are loaded at load/runtime
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# Review
* Really easy to link a library
* Toss `-lname` _at the end of the compilation command_
  * `-lpng` for `libpng.so` or `libpng.a`
  * `-lm` for `libm.so` or `libm.a`
* (Linux) `-l:libname.a` is an explicit way to specify library file to link
* `-Ldir` can specify additional directories to look for libraries
  * You can also link against a library by providing the path to the library
    file as an argument (particularly useful for static libraries)
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# Exercise
* Download the following [file](https://www.eecs.umich.edu/courses/eecs201/sp2026/files/examples/lib.tar.gz)

```bash
https://www.eecs.umich.edu/courses/eecs201/sp2026
|- /files/examples/lib.tar.gz
```
* Compile with `make` and run:

```bash
$ make
g++ -g -std=c++20 -o calc.exe calc.cpp
$ ./calc.exe
calc> 3 + 7
10
```
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# Exercise
* It would be nice to add features such as using the up/down keys to
  scroll through input history, using left/right to navigate a line,
  and so on
  * The standard Python interpreter has these features, for example
* Luckily, there's a library for that: `readline`
  * It's probably already installed on your machine
  * Find documentation for how to modify `calc.cpp` to incorporate
    `readline`
  * Edit the `Makefile` to properly compile with the `readline`
    library
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# Review
### Creating a library
* Create object code with `-c`
  * e.g. `gcc -c -o file.o file.c`
* Dynamic library object code requires `-fPIC` flag
  * e.g. `gcc -c -fPIC -o file.o file.c`
* Static: `ar rcs libname.a file.o`
* Dynamic: `gcc -shared -o libname.so file.o`
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