C# 讀寫 INI 檔案：呼叫 Win32 API (WritePrivateProfileString/GetPrivateProfileString)

.NET 早期版本未內建 INI 檔案操作類別，常見做法是透過 P/Invoke 呼叫 Kernel32.dll 的 WritePrivateProfileString 與 GetPrivateProfileString。本文提供完整封裝類別與使用範例。

P/Invoke 宣告

using System;
using System.Runtime.InteropServices;
using System.Text;

public static class IniFile
{
    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern long WritePrivateProfileString(
        string lpAppName, string lpKeyName, string lpString, string lpFileName);

    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern int GetPrivateProfileString(
        string lpAppName, string lpKeyName, string lpDefault,
        StringBuilder lpReturnedString, int nSize, string lpFileName);

    // 公開靜態方法
    public static void WriteValue(string filePath, string section, string key, string value)
    {
        WritePrivateProfileString(section, key, value, filePath);
    }

    public static string ReadValue(string filePath, string section, string key, string defaultValue = "")
    {
        var sb = new StringBuilder(255);
        GetPrivateProfileString(section, key, defaultValue, sb, sb.Capacity, filePath);
        return sb.ToString();
    }
}

使用範例

string exePath = System.Windows.Forms.Application.ExecutablePath;
string iniPath = System.IO.Path.ChangeExtension(exePath, ".ini"); // 同目錄同名 .ini

// 寫入
IniFile.WriteValue(iniPath, "Database", "Server", "localhost");
IniFile.WriteValue(iniPath, "Database", "Port", "1433");
IniFile.WriteValue(iniPath, "Database", "User", "sa");
IniFile.WriteValue(iniPath, "Settings", "AutoBackup", "true");

// 讀取
string server = IniFile.ReadValue(iniPath, "Database", "Server");
string port   = IniFile.ReadValue(iniPath, "Database", "Port");
bool autoBak  = bool.Parse(IniFile.ReadValue(iniPath, "Settings", "AutoBackup", "false"));

Console.WriteLine($"Server={server}, Port={port}, AutoBackup={autoBak}");

生成的 INI 檔案內容

[Database]
Server=localhost
Port=1433
User=sa

[Settings]
AutoBackup=true

進階封裝：強型別與區段列舉

public class IniFile
{
    private readonly string _path;

    public IniFile(string path) => _path = path;

    public void Write(string section, string key, string value)
        => WritePrivateProfileString(section, key, value, _path);

    public string Read(string section, string key, string defaultValue = "")
    {
        var sb = new StringBuilder(255);
        GetPrivateProfileString(section, key, defaultValue, sb, sb.Capacity, _path);
        return sb.ToString();
    }

    public T Read<T>(string section, string key, T defaultValue = default)
    {
        string val = Read(section, key, null);
        if (val == null) return defaultValue;
        return (T)Convert.ChangeType(val, typeof(T));
    }

    // 列舉所有區段 (需呼叫 GetPrivateProfileSectionNames)
    [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
    private static extern int GetPrivateProfileSectionNames(IntPtr lpszReturnBuffer, int nSize, string lpFileName);

    public string[] GetSections()
    {
        int maxSize = 1024;
        while (true)
        {
            var buffer = Marshal.AllocHGlobal(maxSize);
            int size = GetPrivateProfileSectionNames(buffer, maxSize, _path);
            if (size == 0) { Marshal.FreeHGlobal(buffer); return Array.Empty<string>(); }
            if (size < maxSize - 2)
            {
                string all = Marshal.PtrToStringAuto(buffer, size);
                Marshal.FreeHGlobal(buffer);
                return all.Split(new[] { '\0' }, StringSplitOptions.RemoveEmptyEntries);
            }
            Marshal.FreeHGlobal(buffer);
            maxSize *= 2;
        }
    }
}

替代方案：純 .NET INI 解析器

若不想依賴 P/Invoke，可使用 NuGet 套件 IniParser：

var parser = new FileIniDataParser();
IniData data = parser.ReadFile("config.ini");
string val = data["Database"]["Server"];
data["Settings"]["Theme"] = "Dark";
parser.WriteFile("config.ini", data);

注意事項

• INI 檔案大小限制約 64 KB (Windows 限制)，大型設定請改用 XML/JSON/SQLite。
• 多執行緒同時寫入同一 INI 可能導致資料損毀，需自行加鎖。
• CharSet = CharSet.Auto 可自動依平台選擇 ANSI/Unicode 版 API。