smol_json

A single-header, tiny, non-allocating, streamed JSON parser library for modern C++

Features

• Single header
• Zero heap allocations
• Incredibly fast iterator access
• No exceptions

Examples

Constructing a parser:

smol_json::Parser parser(std::string_view("[ 1, 2 ]"));

Reading a simple string-keyed json object:

{ "integer_key": 42, "boolean_key": false }

bool success = parser.stringKeyIter([&](auto key) {
	if (key == "integer_key" && parser.expectInt())
		printf("integer_key is %i\n", parser.getInt());
	else if (key == "boolean_key" && parser.expectBool())
		printf("boolean_key is %s\n", parser.getBool() ? "ON" : "OFF");
	else return false;

	return true;
});

Output:

integer_key is 42
boolean_key is OFF

Parsing an array:

[ -1, true, { ... } ]

bool success = parser.arrayIter([&](int index) {
	if (!parser.readTok()) return false;

	printf("[%i] ", index);

	if (parser.isInt())
		printf("%i\n", parser.getInt());
	else if (parser.isBool())
		printf("%s\n", parser.getBool() ? "ON" : "OFF");
	else if (parser.isObject())
		return parse_some_object(parser);
	else
		return printf("Error.\n") && false;

	return true;
});

Configuration

SMOL_JSON_DEBUG:

• Define this to enable assertions.

SMOL_JSON_ABORT(msg):

• Define this for a user abort function.
• Called when SMOL_JSON_DEBUG is defined and an assertion fails.

SMOL_JSON_LOG_FN(msg, ...):

• Define this for a user log function.
• Only called when SMOL_JSON_DEBUG is defined.
• Defaults to printf with message prefix "[smol_json] ".

SMOL_JSON_STRING_VIEW:

• Define this to std::string_view/eastl::string_view.
• Defaults to internal implementation smol_json::string_view

Classes

smol_json::string_view:

• Simple string_view implementation for standalone.
• Implements generic comparison operators against any class that implements data() and length().

smol_json::Stream:

• Simple stream based on a string_view.

smol_json::Token:

• A simple token type.
• When read, values are not cleared immediately: reading a string and then a colon will still keep the string value.

smol_json::Lexer(smol_json::Token, smol_json::Stream):

• Simple JSON lexer. Currently does not support floating point data.

smol_json::Parser(smol_json::Lexer):

• Simple JSON parser interface.
• Defines easy iterative APIs