c-and-fortran.Rmd

# C and Fortran code {#c-fortran}

If the package contains C or Fortran code, it should adhere to the standards and
methods described in the [System and foreign language interfaces][CRAN foreign]
section of the [Writing R Extensions][] manual.

We emphasize particular points in the following sections.

### Internal functions

Use internal <i class="fab fa-r-project"></i> functions, e.g., `R_alloc` and random number generators (RNGs), over system-supplied ones.

### C function registration

Use C function registration (See the [Registering native routines][] section of
the [Writing R Extensions][] manual).


### Checks for user interruption

Use `R_CheckUserInterrupt()` in C level loops when there is a chance that they may not terminate for certain parameter settings or when their run time exceeds 10 seconds with typical parameter settings, and the method is intended for interactive use.

### Makevars

Make judicious use of the `Makevars` and `Makefile` files within a package.
These are often not required at all (See the [Configure and cleanup][CRAN config] section of the [Writing R Extensions][] manual).

### Warnings and optimizations

During package development, enable all warnings and disable optimizations.
If you plan to [use a debugger](#debugging-cc-code), tell the compiler to
include debugging symbols.

The easiest way to enforce these is to create a user-level `Makevars` file user’s home directory in a sub-directory called ‘.R’). See examples below for flags for common toolchains.
Consult the section about [Makevars files][] in the [Writing R Extensions][] manual.

Example for gcc/g++:

```
CFLAGS=-Wall -Wextra -pedantic -O0 -ggdb
CXXFLAGS=-Wall -Wextra -pedantic -O0 -ggdb
FFLAGS=-Wall -Wextra -pedantic -O0 -ggdb
```

Example for clang/clang++:

```
CFLAGS=-Weverything -O0 -g
CXXFLAGS=-Weverything -O0 -g
FFLAGS=-Wall -Wextra -pedantic -O0 -g
```