！壞人必需做好事！

# 只能轉與系統同編碼的ansi
function tounicode($orginFile = $(throw "input file required"))
{
 $data = get-content $orginFile
 set-content -value $data $orginFile -encoding utf8
}

# 可以自定來源編碼
function tounicode($orginFile = $(throw "input file required"), $coding = 'Shift-JIS')
{
 #$data = get-content $orginFile
 #set-content -value $data $orginFile -encoding utf8
 #$orginFile = ($pwd).path + "\" + $orginFile;
 $targetFile = $orginFile + "_tmp_";
 $rr=New-Object IO.StreamReader($orginFile,[Text.Encoding]::GetEncoding($coding));
 $ww=New-Object IO.StreamWriter($targetFile, $false, [Text.Encoding]::GetEncoding('UTF-8'));
 while(!$rr.EndOfStream)
 {$ww.WriteLine($rr.ReadLine());}
 $rr.Close();$ww.Close();
 del $orginFile;
 ren $targetFile $orginFile;
}

dir -r | % {if ($_ -like "*.cpp" -or
  $_ -like "*.c" -or
  $_ -like "*.cc" -or
  $_ -like "*.h" -or
  $_ -like "*.hpp")
  {
   tounicode($_.fullname)
  }
 }

經測試自定來源編碼的轉法不會轉到已經是UTF-8編碼的檔案。