EasyIni

Reflection-based INI Parser for C++26

A lightweight INI parser powered by C++26 compile-time reflection (std::meta).

Using Bloomberg's clang-p2996, EasyIni automatically maps INI files to user-defined structs without registration, macros, or manual binding code.

struct Config {
    std::string host;

    [[=range(0,65535)]]
    int port;

    [[=default_value(false)]]
    bool debug;
};

Config cfg;
IniParser::parse("config.ini", cfg);

---

Highlights

• Zero registration or binding code
• Compile-time reflection (std::meta)
• Automatic section-to-struct mapping
• Annotation-based customization
• Built-in validation (range, length, defaults)
• Optional values and enum support
• O(1) field dispatch using compile-time FNV-1a hashing

---

Supported Features

Feature	Annotation	Example
Multi-section mapping	root struct	Root { Server server; Client client; }
Rename section	rename("Server")	[[=rename("Server")]] Config cfg;
Rename field	rename("full_name")	[[=rename("full_name")]] std::string name;
Default value	default_value(v)	[[=default_value(32)]] int age;
Range validation	range(min, max)	[[=range(0,65535)]] int port;
String length validation	length(min, max)	[[=length(0,8)]] std::string code;
Naming convention	naming_convention(Snake)	automatic key conversion
Ignore field	ignore()	skipped during parsing
Optional field	std::optional<T>	key may be omitted
Reject unknown entries	deny_unknown()	unknown keys or sections become errors
Time parsing	time_format("%Y-%m-%d")	std::chrono::sys_days
Enum parsing	automatic	Color::Red ⇄ "Red"

---

Example

struct Person {
    [[=rename("full_name")]]
    std::string name;

    [[=default_value(32)]]
    int age;

    [[=default_value("Chinese")]]
    std::string nationality;
};

struct Server {
    std::string host;

    [[=range(0,65535)]]
    int port;

    [[=default_value(false)]]
    bool debug;
};

struct Config {
    Person person;
    Server server;
};

Config cfg;
IniParser::parse("config.ini", cfg);

---

Benchmark

Benchmark against SimpleIni using a 1000-line INI file, averaged over 100 iterations.

Metric	EasyIni	SimpleIni
Parse + bind	6,918 µs	7,753 µs
Binding code	0 lines	~20 GetValue() calls
Field lookup	Compile-time FNV-1a hash	Runtime string lookup

Results

• ~12% faster than SimpleIni
• Zero manual binding code
• O(1) field lookup via compile-time hashing

---

Requirements

EasyIni currently requires Bloomberg's experimental clang-p2996 compiler with C++26 reflection support.

docker run --rm -it -v .:/work ghcr.io/bloomberg/clang-p2996:latest

cd /work
bash build.sh
./ini_parser