Reading and Writing Values from INI Files with C#

INI files is often used by legacy software. But sometimes also by not so legacy software. So sometimes it is needed to access INI files from .NET/C#, but there is no class or method in .NET/C# that can read or write INI files. But there are some functions in kernel32.dll that can be used by Platform Invoke (PInvoke). These functions (GetPrivateProfileString, GetPrivateProfileSection and WritePrivateProfileString) are provided for compatibility, nevertheless they can be used.

You need to add a using that allows using PInvoke.

using System.Runtime.InteropServices;

Then you can declare the methods that you want to access.

[DllImport("kernel32", CharSet = CharSet.Unicode)]
private static extern int GetPrivateProfileString(string section, string key,
    string defaultValue, StringBuilder value, int size, string filePath);
 
[DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
static extern int GetPrivateProfileString(string section, string key, string defaultValue,
    [In, Out] char[] value, int size, string filePath);
 
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
private static extern int GetPrivateProfileSection(string section, IntPtr keyValue,
    int size, string filePath);
 
[DllImport("kernel32", CharSet = CharSet.Unicode, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool WritePrivateProfileString(string section, string key,
    string value, string filePath);

Now we can use these methods to access an INI file. Therefor we have defined a size into that the results should fit. You can extend or reduce the size as needed.

public static int capacity = 512;

You can read values with the following code.

public static string ReadValue(string section, string key, string filePath, string defaultValue = "")
{
    var value = new StringBuilder(capacity);
    GetPrivateProfileString(section, key, defaultValue, value, value.Capacity, filePath);
    return value.ToString();
}
 
public static string[] ReadSections(string filePath)
{
    // first line will not recognize if ini file is saved in UTF-8 with BOM
    while (true)
    {
        char[] chars = new char[capacity];
        int size = GetPrivateProfileString(null, null, "", chars, capacity, filePath);
 
        if (size == 0)
        {
            return null;
        }
 
        if (size < capacity - 2)
        {
            string result = new String(chars, 0, size);
            string[] sections = result.Split(new char[] { '\0' }, StringSplitOptions.RemoveEmptyEntries);
            return sections;
        }
 
        capacity = capacity * 2;
    }
}
 
public static string[] ReadKeys(string section, string filePath)
{
    // first line will not recognize if ini file is saved in UTF-8 with BOM
    while (true)
    {
        char[] chars = new char[capacity];
        int size = GetPrivateProfileString(section, null, "", chars, capacity, filePath);
 
        if (size == 0)
        {
            return null;
        }
 
        if (size < capacity - 2)
        {
            string result = new String(chars, 0, size);
            string[] keys = result.Split(new char[] { '\0' }, StringSplitOptions.RemoveEmptyEntries);
            return keys;
        }
 
        capacity = capacity * 2;
    }
}
 
public static string[] ReadKeyValuePairs(string section, string filePath)
{
    while (true)
    {
        IntPtr returnedString = Marshal.AllocCoTaskMem(capacity * sizeof(char));
        int size = GetPrivateProfileSection(section, returnedString, capacity, filePath);
 
        if (size == 0)
        {
            Marshal.FreeCoTaskMem(returnedString);
            return null;
        }
 
        if (size < capacity - 2)
        {
            string result = Marshal.PtrToStringAuto(returnedString, size - 1);
            Marshal.FreeCoTaskMem(returnedString);
            string[] keyValuePairs = result.Split('\0');
            return keyValuePairs;
        }
 
        Marshal.FreeCoTaskMem(returnedString);
        capacity = capacity * 2;
    }
}

You can write values with the following code.

public static bool WriteValue(string section, string key, string value, string filePath)
{
    bool result = WritePrivateProfileString(section, key, value, filePath);
    return result;
}

Sections and keys will be created, if they not exist.

Or you can delete values with the following code.

public static bool DeleteSection(string section, string filepath)
{
    bool result = WritePrivateProfileString(section, null, null, filepath);
    return result;
}
 
public static bool DeleteKey(string section, string key, string filepath)
{
    bool result = WritePrivateProfileString(section, key, null, filepath);
    return result;
}