C#获取和设置系统的默认打印机，使用API

既然是API的方式，那首先就是API的引用声明了。

using System.Runtime.InteropServices;

[DllImport("Winspool.drv", CharSet = CharSet.Auto, SetLastError = true)]
private static extern bool SetDefaultPrinter(string printerName);

[DllImport("winspool.drv", CharSet = CharSet.Auto, SetLastError = true)]
private static extern bool GetDefaultPrinter(StringBuilder pszBuffer, ref int pcchBuffer);


static string GetDefaultPrinter() {
    const int ERROR_FILE_NOT_FOUND = 2;

    const int ERROR_INSUFFICIENT_BUFFER = 122;

    int pcchBuffer = 0;

    if (GetDefaultPrinter(null, ref pcchBuffer)) {
        return null;
    }

    int lastWin32Error = Marshal.GetLastWin32Error();

    if (lastWin32Error == ERROR_INSUFFICIENT_BUFFER) {
        StringBuilder pszBuffer = new StringBuilder(pcchBuffer);
        if (GetDefaultPrinter(pszBuffer, ref pcchBuffer)) {
            return pszBuffer.ToString();
        }

        lastWin32Error = Marshal.GetLastWin32Error();
    }
    if (lastWin32Error == ERROR_FILE_NOT_FOUND) {
        return null;
    }

    throw new Win32Exception(Marshal.GetLastWin32Error());
}