A C++ Config File Parser

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Introduction

This article describes a small, light-weight parser for structured config files. Unlike INI-Files, config files may be sub-structured arbitrarily deep. Config files support the expansion of symbolic values from previously defined variables and environment variables.

Using the code

Basic usage

Consider the following example config file:

# Environment variables used as expansion symbol
# Note: symbol names are case sensitive
tempFolder = %TEMP%

# already defined variables used as expansion symbol
tempSubFolder = %tempFolder%\config-demo

Parsing is as simple as:

Config config("demo.config", envp);

cout << "tempFolder    = '"
   << config.pString("tempFolder") << "'" << endl;
cout << "tempSubFolder = '"
   << config.pString("tempSubFolder") << "'" << endl;

pString() retrieves an unparsed std::string value. The class Config provides additional methods which try to parse the value as a boolean, double, or int.

Config sub groups

Config files may contain sub-groups, as shown in the following example:

# Sub group example
baseName = Welcome Note
message1 = (
#  strings may use ""; it does not make a difference, however.
   name = "%baseName% 1"
   text = Sample message text
)

message2 = (
   name = %baseName% II
   text = Another sample message text
)

Unlike traditional INI-Files, sub-groups may contain further sub-groups up to an arbitrary depth. A sub-group may be accessed by name, or the whole collection of sub-groups may be accessed as stl::map<string, Config*>&.

The following code shows how to parse all sub-groups starting with a prefix, without knowing the exact count in advance:

// get properties for all subgroups starting with prefix
map<string, Config*> messages = config.getGroups(); // all groups
const string messagePrefix = "message"; // prefix for group name
for (map<string, Config*>::iterator i = messages.begin(); i != messages.
end(); ++i) {
       string groupName = i->first;
       Config* group = i->second;

       // test group name for prefix
       if (groupName.substr(0, messagePrefix.length()) == messagePrefix) {
           // display group contents
           cout << group->pString("name") << ":" << endl;
           cout << "   " << group->pString("text") << endl;
       }
}

With this feature, the parser may be also used for structured input documents other than config files. Unlike XML, the representation is more compact, parsing is simpler, and variable expansion is already included.

The distributed source contains very simple error handling. Warnings and error messages are logged to the console. On severe error, the process is aborted. Integrating the source in a project, one may consider to change this to C++ exception handling, if needed.

Only standard C++ functionality is used, so this code is truly cross platform. MSVS Express 2005 project files are included; manual build was tested successfully with GNU g++/Linux, using:

g++ -o ../configDemo *.cpp

History

• First release.