About
Goal
The goal of monero_c is simple, at least on the surface
Build monero for all platforms
Access monero functions from all languages
Bring in new features used by wallets but still not merged upstream
To achieve these tasks some major changes had to happen to monero.
Building
For the most part contrib/depends directory of monero was used, as it is in perfect shape (that being said it's terrible to debug when something goes wrong). But it doesn't work with iOS, and it doesn't work on macOS, so some dependencies had to be pulled as a submodules. But that being said, linux can be used to build for all platforms (except for iOS - you need macOS for that, and you also need that 100EUR/year license to actually be able to do something with said library).
This is especially good because any device can run linux, on WSL2 or under docker.
Accessing monero functions
Though just building the library is not enough, if you just make wallet_api in the upstream code you end up in a place where you technically have the functions in a dynamic library, but you can only use C++ ABI to interact with it. Which is not ideal. Of course, it is doable, if you want to deal with __ZNK6Monero10WalletImpl7addressEjj instead of MONERO_Wallet_address, and make sure that the way you pass in variables is what C++ expects. I went with the simplest and most standard way of doing that - C ABI (which is what monero should offer in the first place). Now with any language that supports C interop you can just go ahead and use monero wallet.
All functionality is simplified to use only the following types:
bool
int
uint64_t
void*
const char*
void
Bring in new features
There are some extra features inside of the code like
Polyseed support
Background sync
Airgap functions
Coin control
UR support
Ledger support (on android and iSO)
many fixes
These features land in the patches directory, and are applied to the upstream monero code.
Summary
monero_c extends monero functionality and also simplifies it by a huge extent, if you want to use monero - monero_c is probably the way to go. Are you ready to start? Let's see how to build the binary.