perfhash is a perfect hash table generator for C++ (And hopefully later other languages). It's based in part on GNU gperf's internals, but with a completely different interface and API for the generated tables. In particular, instead of a static table, it creates hash table objects so that multiple tables with the same keys can exist in the same program - one per thread, say.

perfhash uses cmake. In the base perfhash directory:

$ mkdir build
$ cd build
$ cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo [OTHER OPTIONS] ../src
$ cmake --build

This creates an executable named perfhash that can be copied whereever.

perfhash takes an input file that is a JSON document whose layout is described below, and creates source code files containing the implementation of a perfect hash or set. Usage is simple:

$ perfhash table_description.json

All options and settings are controlled by the input file.

perfhash can create two types of tables, corresponding roughly to std::unordered_set and std::unordered_map. The keys are always strings, the values if present are an arbitrary user-controlled type.

The JSON file that describes the table to be created. It holds a single JSON object, with the following fields:

Can be either "set" or "map".

Controls the output language, files and language-specific options. The "language" field controls what else is present.

For C++ output, "language" can be "c++17" or "c++14". Older versions are not currently supported.

The key "header file" names the output file (The hash table is a header-only). "class" is used to control the name of the resulting table type. For maps, "value type" is the type of the value. The optional "namespace" field puts the generated classes in the given namespace.

{ "type": "map",
  "output": {
    "language": "c++14",
    "source file": "foo.cpp",
    "header file": "foo.h".
    "class": "my_map",
    "value type": "int"
    },
  "data": [
    {"key": "dog", "value":"1"},
    {"key": "cat", "value":"2"},
    {"key": "rat", "value":"3"}
    ]
}