How write to a txt file using SysUtils.FileWrite api? - delphi

Question

I'm want write name of my pc to a txt file using SysUtils.FileWrite api, in my last attempt is wrote with sucess, but the trouble is that visually is cutting some characters, but size of text inside file have exactly the same size as if string is complete visually.
Eg: My pc is called of "TESTE-PC" (Without double quotes). The string "TESTE-PC" (Without double quotes) have exactly 8 bits, but SysUtils.FileWrite writes only "TEST" and size of file after is 8 bits. Very strange! :(
Thank you for any suggestion.
uses
Registry;
...
function GetCompName: string;
var
Reg: TRegistry;
begin
Reg := TRegistry.Create;
try
Reg.rootKey := HKEY_LOCAL_MACHINE;
if Reg.OpenKey('SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName', false) then
begin
Result := Reg.ReadString('ComputerName');
Reg.CloseKey;
end;
finally
Reg.Free;
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
var
hFile: THandle;
Str: PWideChar;
begin
if not fileexists('test.txt') then
begin
Str := PWideChar(GetCompName);
hFile:= CreateFile('test.txt', GENERIC_WRITE, 0, nil, OPEN_ALWAYS, FILE_FLAG_WRITE_THROUGH, 0);
FileWrite(hFile, Str^, Length(Str));
CloseHandle(hFile);
end;
end;

Answer 1

First off, using the Registry to get the computer name is wrong. Use the GetComputerName() function instead:
uses
Windows;
...
function GetCompName: string;
var
CompName: array[0..MAX_COMPUTERNAME_LENGTH] of Char;
Size: DWORD;
begin
Size := Length(CompName);
if GetComputerName(CompName, Size) then
SetString(Result, CompName, Size-1)
else
Result := '';
end;
Second, your FileWrite() code fails because you are not handling character encodings correctly. FileWrite() operates on raw bytes only, but you are working with Unicode strings and not taking into account that SizeOf(WideChar) is 2, not 1 like your code assumes.
You should also be using the RTL's FileCreate() function with FileWrite(). If you use the Win32 CreateFile() function directly, you should be using the Win32 API WriteFile() directly as well.
And no matter how you choose to write the file, you should be using an absolute path to the file, never a relative path.
Try something more like this:
procedure TForm1.FormCreate(Sender: TObject);
var
FileName: string
hFile: THandle;
Str: string;
begin
FileName := 'C:\path to\test.txt';
if not FileExists(FileName) then
begin
Str := GetCompName;
hFile := FileCreate(FileName);
if hFile <> INVALID_HANDLE_VALUE then
begin
FileWrite(hFile, PChar(Str)^, Length(Str) * SizeOf(Char));
FileClose(hFile);
end;
end;
Note that the code above will create the file in UTF-16 encoding. If you wanted to use UTF-8 instead, it would look like this:
procedure TForm1.FormCreate(Sender: TObject);
var
FileName: string;
hFile: THandle;
Str: UTF8String;
begin
FileName := 'C:\path to\test.txt';
if not FileExists(FileName) then
begin
Str := UTF8String(GetCompName);
hFile := FileCreate(FileName);
if hFile <> INVALID_HANDLE_VALUE then
begin
FileWrite(hFile, PAnsiChar(Str)^, Length(Str));
FileClose(hFile);
end;
end;
Or any other encoding, for that matter:
procedure TForm1.FormCreate(Sender: TObject);
var
FileName: string;
hFile: THandle;
Enc: TEncoding;
Str: TBytes;
begin
FileName := 'C:\path to\test.txt';
if not FileExists(FileName) then
begin
Enc := TEncoding.GetEncoding('desired encoding');
try
Str := Enc.GetBytes(GetCompName);
finally
Enc.Free;
end;
hFile := FileCreate(FileName);
if hFile <> INVALID_HANDLE_VALUE then
begin
FileWrite(hFile, PByte(Str)^, Length(Str));
FileClose(hFile);
end;
end;
Whatever encoding you decide to use, a simpler solution would be to use the IOUtils.TFile.WriteAllText() method instead:
uses
IOUtils;
procedure TForm1.FormCreate(Sender: TObject);
var
FileName: string;
begin
FileName := 'C:\path to\test.txt';
if not FileExists(FileName) then
begin
TFile.WriteAllText(FileName, GetCompName, TEncoding.UTF8); // or TEncoding.Unicode, etc...
end;
end;

Answer 2

If you need to write wide chars, take their size into account:
FileWrite(hFile, Str^, Length(Str) * SizeOf(Char));

Answer 3

Change the type of str to RawByteString instead of PWideChar
procedure TForm1.FormCreate(Sender: TObject);
var
hFile: THandle;
sFileName: string;
Str: RawByteString;
begin
Str := PWideChar(GetCompName);
sFileName := 'Test.txt';
if fileExists(sFileName) then
hFile := fileOpen(sFileName,fmOpenReadWrite)
else
hFile := fileCreate(sFileName);
try
FileWrite(hFile,
PChar(Str)^, Length(Str));
finally
FileClose(hFile);
end;
end;