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A small, storage-agnostic C++14 localization library.
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This is a simple internationalization library. It is designed to be storage-agnostic; language files can be stored in any way appropriate for your platform and OS. It's also designed to be lean while remaining flexible.


libsn is designed to be embedded directly in other applications. There is no provision for building it as a stand-alone library.

Include the following source files in your build:

  • Mandatory. Contains all core functionality of the library.
  • Optional. Contains the implementation of SN::Context::GetSystemLanguage. You will probably want this.
  • Optional. Contains the SN::FileCatSource implementation for OSes with POSIX-like paths and a dirent implementation. (Everything but Windows, these days.)
  • This file doesn't exist, but it's where the SN::FileCatSource implementation for Windows would live if it did.

libsn makes use of C++14 features. Most compilers must be specially instructed to compile in C++14 mode. For gcc/clang, pass -std=c++14.


This section assumes that you are familiar with good internationalization practice in general, and does not try to teach the basics.

#include "sn.hh"

Keep an SN::Context instance somewhere, conventionally in a global named sn.

Before use, call sn.AddCatSource(...), passing some instance of SN::CatSource. For simple purposes, a SN::FileCatSource will do. (Note that there is not a Windows implementation of SN::FileCatSource yet.) Its constructor takes a path to a directory full of catalog files, where <LANG>.utxt contains the translations for the language with IETF language code <LANG>. libsn will get confused if a file contains a language that doesn't match its filename. If you want a different filename suffix, pass it as the second parameter to FileCatSource's constructor. If the path does not contain a trailing directory separator, the final component of the path will be used as a filename prefix.

If you wish to use more than one CatSource, you may call sn.AddCatSource more than once. This might be useful for plugins, modifications, or even just for organization purposes. Call sn.ClearCatSource to forget all previously-added CatSources. If translations for the same message are provided by more than one CatSource, the CatSource added last takes priority.

Call sn.SetLanguage(...), passing the IETF language code you wish to use. For most purposes, you want to do sn.SetLanguage(sn.GetSystemLanguage()), thus selecting the best available match for the user's system language. sn.GetSystemLanguage() will return a default language (en-US unless a different code is passed as a parameter) if there are no cats available in any of the user's preferred languages.

Only the CatSources that were active the most recent time sn.SetLanguage(...) was called will take effect. If sn.SetLanguage(...) evaluates to false, no messages were loaded.

At this point, the context is ready for use. When you need a translated string, call sn.Get("..."_Key). If the string requires substitutions, pass a braced list of substitutions as an additional parameter. If you want to output to a std::ostream directly, without going through a std::string, use sn.Out and pass the ostream as the first parameter. sn.Get and sn.Out are thread-safe.

On the rare occasion you need to fetch a translated string based on a dynamically-generated key, create an instance of SN::ConstKey or SN::DynamicKey. ConstKey does not own its string, whereas DynamicKey makes a copy of the string and owns that copy. (_Key is a string literal suffix that pre-computes a ConstKey at compile time, if, like recent GCC, your compiler is smart enough.)

On the even rarer occasion you need to detect whether a key is missing or not, you can call sn.Lookup, which will return nullptr if the key is missing. In general, you shouldn't do this; use tools to check the completeness of translations instead.


C++ source file:

#include "sn.hh"
#include <iostream>
#include <string>

SN::Context sn;

int main(int argc, char** argv) {
    // don't forget the trailing slash!
    if(!sn.SetLanguage(sn.GetSystemLanguage())) {
        std::cerr << "Unable to load any language files.\n";
        return 1;
    std::cout << sn.Get("MESSAGE_1"_Key) << "\n";
    // MESSAGE_2 contains a trailing newline, unlike the other messages
    sn.Out(std::cout, "MESSAGE_2"_Key);
    std::cout << sn.Get("NUM_ARGS"_Key, {std::to_string(argc)}) << "\n";
    for(int n = 0; n < argc; ++n) {
        std::cout << sn.Get("ARG"_Key,
                             std::to_string(n)}) << "\n";
    std::cout << sn.Get("NO_MORE_ARGS"_Key) << "\n";
    std::string keystr = std::string("SIZEOF_INT_")
                         + std::to_string(sizeof(int));
    SN::ConstKey key(, keystr.length());
    std::cout << sn.Get(key) << "\n";
    return 0;

Catalog file en.utxt:

: A line beginning with a colon is a comment. Blank lines are ignored, except
: inside a message. A line beginning with a colon, or consisting of a single
: period, can be escaped with a leading backslash.

: A message catalog begins with MIME-like headers. Unrecognized headers are
: ignored. The file should be in whatever the application's native character
: set is; if that character set isn't UTF-8, you'd better have a darned good
: reason for it.

: Language-Code specifies the IETF language code presented in this file. The
: filename must match this language code.
Language-Code: en
: Language-Name gives the name readers of this language will know it by.
: This will be useful in a future version of the library, which will
: contain a way for programs to access the list of available languages.
Language-Name: English
: Language-Name-en gives the name an English speaker would know this language
: by. Names in other languages can be given, too, by using different language
: codes. This header is useful for coordinating translation efforts. If this
: is an English catalog, the value of Language-Name is used, and this header
: is optional.
Language-Name-en: English
: If a Fallback header is present, the specified language code will be used to
: "fill in" any gaps in the catalog. For example, a British English (en_GB)
: catalog could translate only strings where spelling differs from American
: English (en_US), and specify en_US as the Fallback language. If no Fallback
: header is provided, the library has some simple fallback logic which is
: usually adequate.
: The fallback language should ideally be one which is intelligible to readers
: of the primary language of this catalog.
Fallback: eo

A nonblank line starts a message. Subsequent lines, up to a line containing
only a period, form the message.

A message does not include the trailing linebreak, but can include a number of
blank lines.
In order for a message to contain a trailing newline, it must end with a blank
line. (Like this message does.)


Value of argc is: $1

Argument #$2: $1

End of argument list.

Your compiler has a 16-bit int.

Your compiler has a 32-bit int.

Your compiler has a 64-bit int.

If a __MISSING_KEY__ message is provided, failed lookups will use it. The
key whose lookup failed will be passed as \$1. If no __MISSING_KEY__ is
present in any catalog, a default obtrusive placeholder will be used.
This message shouldn't be seen in the output of the test program, except
maybe if the size of an int is strange.
In case it is seen, the missing key was: $1


$ ./sntest Argument
A nonblank line starts a message. Subsequent lines, up to a line containing
only a period, form the message.
A message does not include the trailing linebreak, but can include a number of
blank lines.
In order for a message to contain a trailing newline, it must end with a blank
line. (Like this message does.)
Value of argc is: 2
Argument #0: ./sntest
Argument #1: Argument
End of argument list.
Your compiler has a 32-bit int.
You can’t perform that action at this time.