README

📝 LogManager

A lightweight, single-unit logging library for Free Pascal / Lazarus.

📖 Overview

LogManager is a drop-in Pascal unit that provides a single class, TLogManager, for writing timestamped log entries to a file or to the console. It supports:

• 🎚️ Log levels (Normal, Verbose, Debug) that filter which messages are written
• 🏷️ Log types (Notify, Info, Warning, Error, FatalError, Debug)
• 🔄 Automatic log rotation once a log file reaches a configurable size (LogMaxSize, 10 MB by default)
• 🛟 Fallback output to the console if writing to the log file fails
• 🌍 Cross-platform paths via DirectorySeparator and LazFileUtils

📦 Requirements

🚀 Installation

1. Copy logmanager.pas into your project (or add its folder to the unit search path).
2. In Lazarus, add LazUtils as a required package: Project → Project Inspector → Add → New Requirement → LazUtils.
3. Add LogManager to your uses clause. The unit sets {$mode objfpc}{$H+} itself, so it also builds with plain fpc.

uses
  LogManager;

⚡ Quick start

program Demo;

uses
  SysUtils, LogManager;

var
  Log: TLogManager;
begin
  Log := TLogManager.Create(lmFile);
  try
    Log.Module       := 'MyApp';              // file name will be MyApp.log
    // LogDirectory defaults to the application's directory
    Log.LogLevel     := llVerbose;
    Log.LogMaxSize   := 5 * 1024 * 1024;     // rotate at 5 MB (default 10 MB)
    Log.Fallback     := True;                 // fall back to console on file errors

    Log.WriteLog(ltInfo,    'Application started');
    Log.WriteLog(ltWarning, 'Config file not found, using defaults');
    Log.WriteLog(ltDebug,   'Not written: level is Verbose');
    Log.WriteLog(ltError,   'Could not connect to database');
  finally
    Log.Free;
  end;
end.

Resulting MyApp.log:

[20/10/2026 15:45:01]MyApp- [Info] Application started
[20/10/2026 15:45:01]MyApp- [Warning] Config file not found, using defaults
[20/10/2026 15:45:01]MyApp- [Error] Could not connect to database

The timestamp is produced by DateTimeToStr(Now), so its format follows the system locale.

⚙️ How it works

Architecture

             ┌──────────────────────┐
  WriteLog ─▶│  LogMode?            │
             └─────┬──────────┬─────┘
             lmFile│          │lmConsole
                   ▼          ▼
           WriteLogFile   WriteLogConsole ──▶ stdout
                   │
        ┌──────────┴───────────┐
        │ file ≥ LogMaxSize?   │
        └──┬────────────────┬──┘
        yes│                │no
           ▼                ▼
   rename to Module-N.log   load file, append entry
   start a fresh file       save file
           │
     on exception ──▶ Fallback? ──▶ WriteLogConsole

Log levels

The LogLevel property decides which log types actually get written:

llNormal is the default.

File output

• Log file path: <LogDirectory>/<Module>.log. LogDirectory defaults to the directory of the running executable, resolved from ParamStr(0), which works on every platform. The directory is not created automatically.
• On every write, the existing file is loaded into an internal TStringList, the new line is appended, and the file is saved back.
• Entry format: [<timestamp>]<Module>- [<Type>] <message>

Log rotation

Before writing, the file size is checked. If it is ≥ LogMaxSize bytes (default 10 * 1024 * 1024 = 10,485,760 bytes, 10 MB):

1. The current file is renamed to the first free name among <Module>-1.log, <Module>-2.log, … <Module>-2048.log.
2. The new entry is written to a fresh <Module>.log.

Fallback

If an exception occurs while writing the log file and Fallback = True:

Console output

• WriteLog with LogMode = lmConsole prints [<timestamp>]<Module>-<Type><message> via WriteLn.
• WriteLogAndConsole prints a short, Portuguese-labelled line to the console and, when LogMode = lmFile, also writes the entry to the log file. Both respect LogLevel. In lmConsole mode each message is printed once.

  	Type
  	ltNotify
  	ltInfo
  	ltWarning
  	ltError
  	ltFatalError
  	ltDebug

📚 API reference

Types

TLogMode  = (lmFile = 1, lmConsole = 2);
TLogType  = (ltNotify = 0, ltInfo = 1, ltWarning = 2, ltError = 3,
             ltFatalError = 4, ltDebug = 5);
TLogLevel = (llNormal = 0, llVerbose = 1, llDebug = 2);

TLogManager

📄 License

Distributed under the MIT License. See LICENSE for details.

© 2025 Rodrigo Peetz