#api #ffi #no-std #no-std

sys no-std nstd-sys

Cross platform general purpose C library written in Rust

20 releases (12 breaking)

new 0.13.0 Feb 17, 2024
0.11.0 Nov 23, 2023
0.8.0 Jul 20, 2023
0.5.0 Mar 16, 2023
0.3.3 Nov 27, 2022

#78 in Memory management

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MIT license

7.5K SLoC


A cross-platform, fast, and safe general purpose C library written in Rust.

The library is organized as a series of modules. The top level module nstd encompasses the entire crate. Each module can have their own submodules (eg. nstd.io.stdout or nstd::io::stdout with Rust syntax).

Example using C

// Build nstd with features set to "capi core io".
#include <assert.h>
#include <nstd.h>

/// Main entry point of the program.
int main(void) {
    const NSTDOptionalStr output_opt = nstd_core_str_from_raw_cstr("Hello, 🌎!");
    const NSTDStr output = output_opt.value.some;
    const NSTDIOError err = nstd_io_print_line(&output);
    assert(err == NSTD_IO_ERROR_NONE);
    return 0;

Library modules

  • nstd - A cross-platform, fast, and safe general purpose C library written in Rust.
    • alloc - Low level memory allocation.
    • core - Provides core functionality for nstd.
      • alloc - Provides useful types for memory allocation support.
      • cstr - Unowned C string slices.
        • raw - Raw C string processing.
      • cty - Provides functions for examining and operating on character types.
      • def - Contains common types used throughout nstd.
      • fty - Provides functions for examining and operating on floating point types.
      • ity - Provides functions for examining and operating on integral types.
      • math - Low level math operations.
      • mem - Contains mostly unsafe functions for interacting with raw memory.
      • ops - Operator overloading for types and operators that may cause overflow.
      • optional - Represents an optional (possibly uninitialized) value.
      • ptr - A sized pointer to some arbitrary type.
      • range - A numerical range.
      • result - Defines a "result" type with success and error variants.
      • slice - A view into a sequence of values in memory.
      • str - An unowned view into a UTF-8 encoded byte string.
      • time - Low level time utilities.
      • unichar - A Unicode scalar value.
    • cstring - A dynamically sized, null terminated, C string.
    • env - Process environment management.
    • fs - Provides access to the file system.
      • file - A handle to an opened file.
    • heap_ptr - A pointer type for single value heap allocation.
    • io - Provides functionality for interacting with the standard I/O streams.
      • stderr - A handle to the standard error stream.
      • stdin - A handle to the standard input stream.
      • stdout - A handle to the standard output stream.
    • math - High level math operations.
    • mutex - A mutual exclusion primitive useful for protecting shared data.
    • os - Operating system specific functionality.
      • unix - Low level Unix-like operating system support.
        • alloc - Memory allocation for Unix-like systems.
        • io - Provides functionality for working with input & output on Unix platforms.
        • mutex - A mutual exclusion primitive useful for protecting shared data.
        • shared_lib - Provides shared library access for Unix-like systems.
        • time - Unix time utilities.
      • windows - OS support for Windows.
        • alloc - Low level memory allocation for Windows.
          • heap - Process heap management for Windows.
        • shared_lib - Shared library/module access for Windows.
        • str - String slice extensions for Windows.
    • proc - Calling/Child process management.
    • shared_lib - Access symbols from loaded shared libraries.
    • shared_ptr - A reference counting smart pointer.
    • string - Dynamically sized UTF-8 encoded byte string.
    • thread - Thread spawning, joining, and detaching.
    • time - Time utilities.
    • timed_mutex - A mutual exclusion primitive with a timed locking mechanism.
    • vec - A dynamically sized contiguous sequence of values.

Platform support

nstd.core should support anything that the Rust compiler supports. This module has first class support for bare metal environments.

nstd.os's child modules will only work on the operating system they target. For example, nstd.os.windows will only work on Windows and nstd.os.unix will only work on Unix-like systems.

Other modules will work on most platforms, primarily targeting Windows, macOS, Linux, Android, and iOS.

Language support

This library can be accessed from any language that supports calling C code. As of now this will need to be done manually as there are no official wrappers for the API, however when the API becomes more stable, the plan is to start adding official wrappers so developers from other languages can easily use the API.


Please note that these safety notes (as well as the framework as a whole) are a work in progress.

User safety notes

  • Raw pointers are unsafe to access.

  • References are assumed to be valid (aligned, non-null, and non-dangling), and are safe to access. Users can refer to the docs to see which APIs expect or return valid references.

  • C function pointers are assumed to be non-null unless wrapped in an Option.

  • Private (non-pub) structure members must not be directly accessed by the user.

  • Tagged enum variants must be checked before they're accessed (eg. NSTDOptional or NSTDResult types).

  • Data is moved when using the value-copy semantic on a type that does not implement Copy.

  • Data must not be moved or mutated while being referenced by another object.

  • Types that do not implement the Send trait must not be sent between threads.

  • Types that do not implement the Sync trait must not be shared between threads.

Contributor safety notes

  • Any operation that may cause undefined behavior must be marked unsafe.

  • All C function pointers taken as input by the API must be marked unsafe.

  • The panic behavior is set to abort by default, as it is undefined behavior to unwind from Rust code into foreign code (though this is subject to change).

How to build

Building nstd as a C library requires you to specify the "crate-type" manually. To do this you must pass a --crate-type of either cdylib or staticlib to rustc. Rust allows you to use this flag multiple times in case you need both.

nstd lets you decide what features you want to use.

Any module that falls under the top level module has a dedicated feature flag, for example nstd.core has the feature flag core and nstd.alloc has the feature flag alloc.

Each module may have additional features, for example nstd.os has the additional os_windows_alloc feature for memory allocation on Windows, this allows other modules to use the low level memory allocation API for Windows without enabling memory allocation for other operating systems.

The std feature flag links the Rust standard library into the binary.

The capi feature flag is used to build nstd as a C library.

The link feature flag will link to an existing nstd library on the system. This feature is encouraged but not required to be enabled for Rust crates that use nstd's capi feature.

std and core are enabled by default.


cargo rustc --release --crate-type cdylib --crate-type staticlib --features "capi alloc string"

To build with all modules enabled:

cargo rustc --release --crate-type cdylib --crate-type staticlib --features "nstd"

Installing with cargo-c

nstd also allows you to use cargo-c to build or install the library.

Install cargo-c:

cargo install cargo-c

Here is an example of how to build the library for a Unix machine with all features enabled:

cargo cinstall --release --all-features --destdir=./install --prefix=/usr --libdir=/usr/lib

This will create a new install directory with the installation contents.

You can now copy the contents to the root folder using cp:

sudo cp -a ./install/* /

More information can be found in the cargo-c repo and in this blog post by Luca Barbato.


nstd versions follow the Semantic Versioning rules. Each release is given a major, minor, and patch number that makes up that version of the library (major.minor.patch).

There have not yet been any major releases for the framework as it is not yet stable.

A new minor version is released every 6 weeks, exactly 1 week after a new minor Rust release.

Patch releases are released every so often with minor fixes and additions.

See semver.org to learn more about Semantic Versioning.


~84K SLoC