SysUtils.FileExists Function

Tests if a specified file exists.

Pascal

function FileExists(const FileName: string): Boolean;

C++

Boolean FileExists(const AnsiString FileName);

File

SysUtils

Description

FileExists returns true if the file specified by FileName exists. If the file does not exist, FileExists returns false.

C++ Examples:

Copy Code

/*
The following example uses a button, a string grid, and a
Save dialog box on a form. When the button is clicked, the
user is prompted for a filename. When the user clicks OK,
the contents of the string grid are written to the specified
file. Additional information is also written to the file so
that it can be read easily with the FileRead function. Verify
the file written after executing.
*/

#include <dir.h>

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  char szFileName[MAXFILE+4];
  int iFileHandle;
  int iLength;
  if (SaveDialog1->Execute())
  {
    if (FileExists(SaveDialog1->FileName))
    {
      fnsplit(AnsiString(SaveDialog1->FileName).c_str(), 0, 0, szFileName, 0);
      strcat(szFileName, ".BAK");
      RenameFile(SaveDialog1->FileName, szFileName);
    }
    iFileHandle = FileCreate(SaveDialog1->FileName);
    // Write out the number of rows and columns in the grid.
    FileWrite(iFileHandle, reinterpret_cast<char *>(&(StringGrid1->ColCount)), sizeof(StringGrid1->ColCount));
    FileWrite(iFileHandle, reinterpret_cast<char *>(&(StringGrid1->RowCount)), sizeof(StringGrid1->RowCount));
    for (int x=0;x<StringGrid1->ColCount;x++)
    {
      for (int y=0;y<StringGrid1->RowCount;y++)
      {
        // Write out the length of each string, followed by the string itself.
        iLength = StringGrid1->Cells[x][y].Length();
        FileWrite(iFileHandle, reinterpret_cast<char *>(&iLength), sizeof(iLength));
        FileWrite(iFileHandle, StringGrid1->Cells[x][y].t_str(), StringGrid1->Cells[x][y].Length());
      }
    }
    FileClose(iFileHandle);
  }
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
  StringGrid1->Cells[1][0] = "Column 1";
  StringGrid1->Cells[2][0] = "Column 2";
  StringGrid1->Cells[3][0] = "Column 3";
  StringGrid1->Cells[4][0] = "Column 4";
  StringGrid1->Cells[0][1] = "Row 1";
  StringGrid1->Cells[1][1] = "Object";
  StringGrid1->Cells[2][1] = "Pascal";
  StringGrid1->Cells[3][1] = "is";
  StringGrid1->Cells[4][1] = "excellent";
  StringGrid1->Cells[0][2] = "Row 2";
  StringGrid1->Cells[1][2] = "Delphi";
  StringGrid1->Cells[2][2] = "is";
  StringGrid1->Cells[4][2] = "RAD";
};

Copy Code

/*
The following code prompts for confirmation before deleting
a file.  Create a file and then click on the button to select
the file with a TOpenDialog.  Click Yes to delete it.
*/
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  OpenDialog1->Title = "Delete File";
  if (OpenDialog1->Execute())
  {
    if (FileExists(OpenDialog1->FileName))
    {
      if (MessageDlg(
        ("Do you really want to delete " + ExtractFileName(OpenDialog1->FileName) + "?"),
        mtConfirmation,
        TMsgDlgButtons() << mbYes << mbNo,
        0,
        mbNo) == mrYes)
        DeleteFile(OpenDialog1->FileName);
    }
    else
      MessageDlg(("File " + ExtractFileName(OpenDialog1->FileName) + " does not exist."), mtConfirmation, TMsgDlgButtons() << mbOK, 0);
  }
}

Copy Code

/*
The following example uses a button, a string grid, and an
Open dialog box on a form. When the button is clicked, the
user is prompted for a filename. When the user clicks OK,
the specified file is opened, read into a buffer, and closed.
Then the buffer is displayed in two columns of the string
grid. The first time you use this app, you should do a "Fill
Grid" and then "Write Grid to File".   Always use files
generated in this way to do a "Read File into Grid".
*/
// Read File to Grid

#include <memory>       //for STL auto_ptr class

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  int iFileHandle;
  int iFileLength;
  int iBytesRead;
  int iLength;
  if (OpenDialog1->Execute())
  {
    try
    {
      iFileHandle = FileOpen(OpenDialog1->FileName, fmOpenRead);
      iFileLength = FileSeek(iFileHandle,0,2);
      FileSeek(iFileHandle,0,0);
      iBytesRead = FileRead(iFileHandle, reinterpret_cast<char *>(&(StringGrid1->ColCount)), 4);
      iBytesRead = FileRead(iFileHandle, reinterpret_cast<char *>(&(StringGrid1->RowCount)), 4);
      for (int x = 0; x < StringGrid1->ColCount; x++)
      {
        for (int y = 0; y < StringGrid1->RowCount; y++)
        {
          // Write out the length of each string, followed by the string itself.
          FileRead(iFileHandle, reinterpret_cast<char *>(&iLength), 4);
          std::auto_ptr<AnsiChar> pszBuffer(new AnsiChar[iLength + 1]);
          FileRead(iFileHandle, pszBuffer.get(), iLength);
          pszBuffer.get()[iLength] = 0;
          StringGrid1->Cells[x][y] = pszBuffer.get();
        }
      }
      FileClose(iFileHandle);
    }
    catch(...)
    {
#if defined(_DELPHI_STRING_UNICODE)
      Application->MessageBox(
        L"Can't perform one of the following file operations: Open, Seek, Read, Close.",
        L"File Error",
        IDOK);
#else
      Application->MessageBox(
        "Can't perform one of the following file operations: Open, Seek, Read, Close.",
        "File Error",
        IDOK);
#endif
    }
  }
}

// Write Grid into File

#include <dir.h>

void __fastcall TForm1::Button2Click(TObject *Sender)
{
  char szFileName[MAXFILE+4];
  int iFileHandle;
  int iLength;
  if (SaveDialog1->Execute())
  {
    if (FileExists(SaveDialog1->FileName))
    {
      fnsplit(AnsiString(SaveDialog1->FileName).c_str(), 0, 0, szFileName, 0);
      strcat(szFileName, ".BAK");
      RenameFile(SaveDialog1->FileName, szFileName);
    }
    iFileHandle = FileCreate(SaveDialog1->FileName);
    // Write out the number of rows and columns in the grid.
    FileWrite(iFileHandle, reinterpret_cast<char *>(&(StringGrid1->ColCount)), sizeof(StringGrid1->ColCount));
    FileWrite(iFileHandle, reinterpret_cast<char *>(&(StringGrid1->RowCount)), sizeof(StringGrid1->RowCount));
    for (int x=0;x<StringGrid1->ColCount;x++)
    {
      for (int y=0;y<StringGrid1->RowCount;y++)
      {
        // Write out the length of each string, followed by the string itself.
        iLength = StringGrid1->Cells[x][y].Length();
        FileWrite(iFileHandle, (AnsiChar *)&iLength, sizeof(iLength));
        FileWrite(iFileHandle, StringGrid1->Cells[x][y].t_str(), StringGrid1->Cells[x][y].Length());
      }
    }
    FileClose(iFileHandle);
  }
}

Delphi Examples:

Copy Code

{
The following example uses a button, a string grid, and a
Save dialog box on a form. When the button is clicked, the
user is prompted for a filename. When the user clicks OK,
the contents of the string grid are written to the specified
file. Additional information is also written to the file so
that it can be read easily with the FileRead function.
} 
procedure TForm1.Button1Click(Sender: TObject);
var
  BackupName: string;
  FileHandle: Integer;
  StringLen: Integer;
  X, Y, I: Integer;
  colCountLength, rowCountLength: Integer;
  Buffer: PChar;
  cellString: string;
begin
  if SaveDialog1.Execute then
  begin
    if FileExists(SaveDialog1.FileName) then
    begin
      BackupName := SysUtils.ExtractFileName(SaveDialog1.FileName);
      BackupName := ChangeFileExt(BackupName, '.BAK');
      if not RenameFile(SaveDialog1.FileName, BackupName) then
        raise Exception.Create('Unable to create backup file.');
    end;
    FileHandle := FileCreate(SaveDialog1.FileName);
    { Write out the number of rows and columns in the grid. }
    colCountLength := SizeOf(StringGrid1.ColCount);
    FileWrite(FileHandle, 
      Pchar(StringGrid1.ColCount), colCountLength);
    rowCountLength := SizeOf(StringGrid1.RowCount);
    FileWrite(FileHandle,
      PChar(StringGrid1.RowCount), rowCountLength);
    for X := 0 to StringGrid1.ColCount - 1 do
    begin
      for Y := 0 to StringGrid1.RowCount - 1 do
      begin
        try
          { Write out the length of each string, followed by the string itself. }
          StringLen := Length(StringGrid1.Cells[X,Y]);
          FileWrite(FileHandle, PChar(StringLen), SizeOf(StringLen));
          GetMem(Buffer, StringLen); { allocate the buffer }
          cellString := StringGrid1.Cells[X,Y];
          for I := 1 to StringLen do
             Buffer[I - 1] := cellString[I];
          FileWrite(FileHandle, Buffer^, StringLen);
        finally
          FreeMem(Buffer, StringLen);
        end;
      end;
    end;
    FileClose(FileHandle);
  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  with StringGrid1 do
  begin
    Cells[1,0] := 'Column 1';
    Cells[2,0] := 'Column 2';
    Cells[3,0] := 'Column 3';
    Cells[4,0] := 'Column 4';
    Cells[0,1] := 'Row 1';
    Cells[1,1] := 'Object';
    Cells[2,1] := 'Pascal';
    Cells[3,1] := 'is';
    Cells[4,1] := 'excellent';
    Cells[0,2] := 'Row 2';
    Cells[1,2] := 'Delphi';
    Cells[2,2] := 'is';
    Cells[4,2] := 'RAD';
  end;
end;

Copy Code

{
The following code prompts for confirmation before deleting
a file.  Create a file and then enter the path and file name
in the textfields.  Click the button to delete it.
}
procedure TForm1.Button1Click(Sender: TObject);
var FileName: string;
begin
  Filename:= Edit1.Text;
  if SysUtils.FileExists(FileName) then
  begin
    if MessageDlg(('Do you really want to delete ' + ExtractFileName(FileName) + '?'), mtConfirmation, [mbYes, mbNo], 0, mbNo) = IDYes then
      DeleteFile(FileName);
  end
  else
    MessageDlg(('File ' + ExtractFileName(FileName) + ' does not exist.'), mtConfirmation, [mbOK], 0);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Edit2.Text:= ExtractFilePath(Application.ExeName);
end;

Copy Code

{
The following example uses a button, a string grid, and an
Open dialog box on a form. When the button is clicked, the
user is prompted for a filename. When the user clicks OK,
the specified file is opened, read into a buffer, and closed.
Then the buffer is displayed in two columns of the string
grid. The first column contains the character values in the
buffer. The second column contains the numeric values of the
characters in the buffer.
}
// Read File to Grid
procedure TForm1.Button1Click(Sender: TObject);
var
  iFileHandle: Integer;
  iFileLength: Integer;
  iBytesRead: Integer;
  Buffer: PAnsiChar;
  X, Y, I: Integer;
  StringLen, colcnt, rowcnt: Integer;
  cellString: String;
begin
  if OpenDialog1.Execute then
  begin
    try
      iFileHandle := SysUtils.FileOpen(OpenDialog1.FileName, fmOpenRead);
      iFileLength := SysUtils.FileSeek(iFileHandle,0,2);
      FileSeek(iFileHandle,0,0);
//      Buffer := PChar(System.AllocMem(iFileLength + 1));
//      iBytesRead := SysUtils.FileRead(iFileHandle, Buffer^, iFileLength);
//      FileClose(iFileHandle);
//      iFileHandle := SysUtils.FileOpen(OpenDialog1.FileName, fmOpenRead);
//      iFileLength := SysUtils.FileSeek(iFileHandle,0,2);
//      FileSeek(iFileHandle,0,0);
      colcnt := StringGrid1.ColCount;
      iBytesRead := SysUtils.FileRead(
        iFileHandle,
        colcnt,
        4);  // 4 because it's an integer
      rowcnt := StringGrid1.RowCount;
      iBytesRead := SysUtils.FileRead(
        iFileHandle,
        rowcnt,
        4);  // 4 because it's an integer
    for X := 0 to StringGrid1.ColCount - 1 do
    begin
      for Y := 0 to StringGrid1.RowCount - 1 do
      begin
        try
          iBytesRead := SysUtils.FileRead(iFileHandle, StringLen, 4);  // 4 because it's an integer
          Buffer := System.AllocMem(StringLen + 1);
//          GetMem(Buffer, StringLen); { allocate the buffer }
          iBytesRead := SysUtils.FileRead(iFileHandle, Buffer^, StringLen);
//          for I := 1 to StringLen do
//            cellString[I] := Buffer[I - 1];
          StringGrid1.Cells[X,Y] := AnsiString(Buffer);
        finally
          FreeMem(Buffer);
        end;
      end;
    end;
    finally
      FileClose(iFileHandle);
    end;
  end;
end;

// Write Grid into File
procedure TForm1.Button2Click(Sender: TObject);
var
  BackupName: string;
  FileHandle: Integer;
  StringLen: Integer;
  X, Y, I: Integer;
  colCountLength, rowCountLength: Integer;
  Buffer: PAnsiChar;
  cellString: AnsiString;
begin
  if SaveDialog1.Execute then
  begin
    if FileExists(SaveDialog1.FileName) then
    begin
      BackupName := SysUtils.ExtractFileName(SaveDialog1.FileName);
      BackupName := ChangeFileExt(BackupName, '.BAK');
      if not RenameFile(SaveDialog1.FileName, BackupName) then
        raise Exception.Create('Unable to create backup file.');
    end;
    FileHandle := FileCreate(SaveDialog1.FileName);
    { Write out the number of rows and columns in the grid. }
    colCountLength := SizeOf(StringGrid1.ColCount);
    FileWrite(FileHandle, 
      PAnsiChar(StringGrid1.ColCount), colCountLength);
    rowCountLength := SizeOf(StringGrid1.RowCount);
    FileWrite(FileHandle,
      PAnsiChar(StringGrid1.RowCount), rowCountLength);
    for X := 0 to StringGrid1.ColCount - 1 do
    begin
      for Y := 0 to StringGrid1.RowCount - 1 do
      begin
        try
          { Write out the length of each string, followed by the string itself. }
          StringLen := Length(StringGrid1.Cells[X,Y]);
          FileWrite(FileHandle, PChar(StringLen), SizeOf(StringLen));
          GetMem(Buffer, StringLen); { allocate the buffer }
          cellString := StringGrid1.Cells[X,Y];
          for I := 1 to StringLen do
             Buffer[I - 1] := cellString[I];
          FileWrite(FileHandle, Buffer^, StringLen);
        finally
          FreeMem(Buffer, StringLen);
        end;
      end;
    end;
    FileClose(FileHandle);
  end;
end;