.NET 1.1+

Reading and Writing INI Files

Initialisation files known as INI files provide a standard means for storing configuration information for software in a text file. Although rarely used by .NET applications, there are situations where these files must be read and written to using C#.

INI Files

Older versions of Microsoft Windows used INI files to store configuration information for the operating system and its applications. These are simple text files that can be edited using software such as Notepad. They hold a series of key / value pairs organised into categories where all of the category names, key names and values are held as strings.

The following shows a sample of the contents of an INI file. The two section names, "Colours" and "Font" are delimited with brackets. The key / value pairs for a section appear below the section name. For example, the Colours section contains a key of "Foreground" with an associated value of "White".

[Colours]
Background=Black
Foreground=White
[Font]
Face=Arial
Size=12pt

Usually, when you create applications using C# and the .NET framework, you will not use INI files. It is more common to store settings in an XML-based configuration file or in the registry. However, if your software shares settings with a legacy application it may be easier to use its configuration file, rather than duplicating the information elsewhere.

The .NET framework does not support the use of INI files directly. However, you can use Windows API functions with Platform Invocation Services (P/Invoke) to write to and read from the files. In this article we will create a class that represents INI files and uses Windows API functions to manipulate them.

Windows API Functions

There are two Windows API functions that we will use to work with INI files. These are named WritePrivateProfileString and ReadPrivateProfileString.

WritePrivateProfileString

WritePrivateProfileString is used to store new and updated settings in an INI file. The signature of the function is:

bool WritePrivateProfileString(
    string lpAppName, string lpKeyName, string lpString, string lpFileName);

The function returns a Boolean value that is true if the write is successful and false if it fails. The parameters are as follows:

• lpAppName. Specifies the name of the section that is to be written to.
• lpKeyName. Specifies the name of the key that is to be set.
• lpString. Specifies the value for the key.
• lpFileName. Specifies the path and name of the INI file to be updated. If the file does not exist, it is created.