VarPar - Variable Parser

VarPar (Variable Parser) is a extremely lightweight C++17+ configuration file parser that provides simple, strict key value parsing for flat text configuration files

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Features

• Strict Parsing: Ensures each key is uniquely defined and every line contains a valid key = value pair
• Automatic Validation: Checks file existence and verifies the correct file extension before parsing
• Informative Error Handling: Reports precise error messages and line numbers for duplicate or malformed entries
• Minimal Dependencies: Uses only standard C++17 libraries
• Lightweight Runtime Status: Parser state (constructed / error) is tracked through ParserStatus for safe checks

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Core Components

vp::Parser

Main parsing class responsible for reading and interpreting configuration files.

Constructor

vp::Parser(const std::string& _id, const std::string& _file, const std::string& _extension = ".varpar");

Parameters

• _id — Unique identifier string for this parser instance.
• _file — File path to the config file.
• _extension — Required file extension (default as: .varpar).

Behavior

• Validates that _file exists.
• Confirms that _file has the required _extension.
• If any checks fail, the parser sets its internal error status and logs the issue to std::cerr.

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ParserReturn

Struct returned by the parser after execution.

struct ParserReturn {
    std::map<std::string, std::string> config;  // Parsed key value pairs
    std::vector<std::string> output;            // Raw messages and errors
    bool success;                               // Parsing result flag
};

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ParserStatus

Represents the parser’s internal construction status.

struct ParserStatus {
    bool constructed;       // Whether parser was constructed successfully
    std::string error;      // Any error message generated during setup
};

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Public Methods

ParserReturn parse()

Executes parsing and returns a structured result. If successful, ParserReturn::success is true and config contains parsed pairs.

std::string getVal(const std::string& _key) const

Retrieves a parsed value by key. Returns an empty string if the key is missing.

ParserStatus checkStatus() const

Returns the internal construction status for validation before parsing.

std::string getID() const

Returns the parser’s unique identifier.

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Parsing Rules

• Lines starting with ; or empty lines are ignored.
• Lines must follow the format:

  key = value

• Whitespace around keys and values is trimmed automatically.
• Duplicate keys produce an immediate error, halting parsing.

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Example File (config.varpar)

; Example config file
hello_world = "Bye..."
random = "aa"
randomText = "aab"

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Example Usage

#include <iostream>
#include <varparse/VP_Parse.hpp>
 
int main()
{
    vp::Parser parse("main-parse", "/path/to/file.varpar");
 
    if (auto status = parse.checkStatus() ; !status.constructed)
    {
        std::cerr << "Failed to construct: " << parse.getID() << "\n";
        std::cerr << status.error << "\n";
 
        std::exit(1);
    }
 
    std::cout << "Output:\n";
 
    vp::ParserReturn parsed = parse.parse();
 
    for (const auto &x : parsed.output)
    { std::cout << x << "\n"; }
 
    if (!parsed.success)
    {
        std::cerr << "[ ! ] Exiting due to an error\n";
 
        std::exit(1);
    }
 
    for (const auto &[k, v] : parsed.config)
    { std::cout << k << " = " << v << "\n"; }
 
    std::cout << "Value of `hello_world`: " << parse.getVal("hello_world") << "\n";
 
    return 0;
}

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Error Example

Given this invalid input:

hello_world = "Bye..."
hello_world = "Bye...a"

Output:

ERR: LINE: 2
Duplicate member : hello_world = "Bye...a"

Due to the fact that there are two keys with the same name

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Supported Compilers

• GCC >= 7.0
• Clang >= 6.0
• MSVC >= 19.14 (Visual Studio 2017 15.7+)

Requires C++17 or newer