tiny_argp

A GNU argp inspired CLI parser for embedded / bare-metal C.

Usage

Copy tiny_argp.c and tiny_argp.h into your project and build them alongside your other sources.

To get started, look at examples/ex1_minimal.c for a minimal working CLI program, then browse the rest of the examples below for options, positional arguments, and subcommands.

Embedded suitability

No allocations

• All state is stack-based or caller-provided.

Minimal stdlib dependency

• Only <stdbool.h> and <stddef.h> (compiler-provided freestanding headers, always available) plus a handful of small routines from <string.h> and <ctype.h> (memcpy, strcmp, strlen, isprint, …) that an embedded libc like newlib-nano or picolibc supplies.

Configurable output

• All output goes through printer / err_printer callbacks, so you provide your own printf and route it to whichever channel your target uses (UART, USB serial, stdout, an in-memory log buffer, etc.). See Printer requirements below.

Never terminates the runtime

• No exit() or similar, errors are returned to the caller.

Printer requirements

All output goes through the printer and err_printer callbacks on the tiny_argp struct. They have a printf-style signature:

typedef int (*tiny_argp_printer_t)(const char *fmt, ...);

The library only ever calls them with the following conversion specifiers:

• %s: null-terminated string
• %c: single character

Any minimal printf implementation that handles %s and %c is sufficient (e.g. mpaland/printf, nanoprintf).

Examples

The examples/ directory contains four self-contained programs.

• examples/ex1_minimal.c: A minimal program with no options and no positional handling. Only has --help and --usage which are added by the library.
• examples/ex2_options.c: A program with a handful of options and no positional arguments.
• examples/ex3_positionals.c: Adds a required positional argument ARG1 and a variable-length list of trailing STRINGs on top of ex2's options. Also has more advanced --help output formatting.
• examples/ex4_subcommands.c: An example using git-style subcommands. An initial parser looks for an add or list subcommands and then calls their parsers with the remaining arguments. Each subcommand has its own options and help output.

Build them all with:

make -C examples

Then invoke any of the binaries directly:

examples/build/ex2_options --help
examples/build/ex3_positionals -v -o /tmp/out A B C
examples/build/ex4_subcommands add --name=widget --count=3

make -C examples verify runs a shell harness that exercises each example with a spread of arg combinations and asserts on exit code and output.

To Test

make -C tests run

Run the test suite with -O0, -Os, -O2, and -O3:

make -C tests matrix

Check binary size

Prints the text / data / bss sizes of the compiled object at the current CFLAGS:

make size

Override optimization level to compare, e.g.:

make clean
make size CFLAGS="-std=c11 -O2"

As a rough reference, on x86_64 with GCC 16.1 the compiled object is around ~12.5 kB with -O0, and ~6.5 kB with -Os.

AI usage

All library code was written by hand.

AI assistance was limited to writing unit tests (reviewed and edited by hand) and copyediting the docs.