C REPL

A simple REPL for the C programming language.

Motivation

Python has an excellent REPL that is very useful to try something quickly. I always wanted something similar for the C programming language. If, for instance, I want to evaluate a simple expression, then why should I write a complete program?

Demo

Other Features

You can also use structs and typedefs:

>>> typedef struct {
...   int x;
...   int y;
... } Pont;
>>>
>>> Pont a = (Pont){1, 2}
>>> %d a.x
1
>>> %d a.y
2

A Python shell is also available if you need it. Quit from the Python shell with Ctrl + d.

>>> _py
Python 3.13.2 (main, Feb  5 2025, 08:05:21) [GCC 14.2.1 20250128] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 2 ** 31 - 1
2147483647
>>>
# C REPL again:
>>> long n = 2147483647
>>> %ld n
2147483647

You can also use a Python one-liner:

>>> (p) hex(2025)
0x7e9
>>> string s = "0x7e9"
>>> %s s
0x7e9

You can also write while loops:

>>> int i = 0
>>> while (i < 3) {
...   puts("hello");
...   ++i;
... }
>>> _run
hello
hello
hello

It's also possible to check for memory leaks with valgrind:

>>> _reset
>>> char *p = malloc(10)
>>> _val
...
==318347== HEAP SUMMARY:
==318347==     in use at exit: 10 bytes in 1 blocks
==318347==   total heap usage: 1 allocs, 0 frees, 10 bytes allocated
...

To simplify reading a text from the keyboard, you can use a "built-in" function called get_string():

>>> string s = get_string("Name: ")
>>> printf("Hello %s!\n", s)
>>>
>>> _run
Name: Laszlo
Hello Laszlo!

If you use this function, then the necessary header file (prog1.h) will be auto-included.

Notes

When I generate the C source code, I add some special comments (e.g. // tmp, // def). I need those comments when I read the modified source code. When you edit the C code with a text editor, I need to parse and re-read the whole source code. These special comments are there to facilitate the parsing. So don't delete these comments!

Installation

I highly encourage using the uv package manager. Then, it's enough to just start ./start.sh, which will (1) create a virt. env. for you, and then (2) start the project.

For Debian-based distros, I made an installer script (setup.sh). Before executing it, verify its content. It installs the uv package manager via pipx, and it also installs some external programs that are used by C REPL (e.g. gcc, valgrind, etc.).

Once everything is installed, just start the launcher script:

$ ./start.sh

Supported Platforms

Tested on Linux only.

The program uses several external Linux commands. They are collected in named constants at the beginning of the source code. Make sure that they are all installed on your system (e.g. gcc, valgrind, etc.)