Chapter 37 Key Takeaways

Environment and Arguments

• GetEnvironmentVariable('NAME') reads environment variables (returns '' if not set)
• ParamStr(0) = executable path; ParamStr(1..ParamCount) = user arguments
• Application data directories differ by platform:
• Windows: %APPDATA%\AppName\
• Linux: $HOME/.config/appname/
• macOS: ~/Library/Application Support/AppName/

File System Operations

• FindFirst / FindNext / FindClose — search for files with wildcards
• ForceDirectories — create entire directory trees (better than CreateDir)
• FileGetAttr — read file attributes (read-only, hidden, etc.)
• Always call FindClose to release search handles

Running External Processes (TProcess)

• TProcess from the Process unit launches external programs
• poWaitOnExit — block until process finishes
• poUsePipes — capture stdout/stderr via Output and Stderr streams
• ExitCode — check the process's return code
• Cross-platform URL opening: start (Windows), xdg-open (Linux), open (macOS)

Conditional Compilation

• Evaluated at compile time, not runtime
• Code in false blocks is completely excluded from the executable
• For large differences, use separate platform-specific units

Calling C Libraries

• function name(params): RetType; cdecl; external 'libname';
• cdecl = C calling convention (mandatory for C interop)
• PChar maps to C's char*; Pointer maps to void*
• Static linking: external 'libname' — library required at compile time
• Dynamic loading: LoadLibrary + GetProcAddress — library loaded at runtime

Platform-Specific Features

PennyWise OS Integration

• FinancePlatform unit encapsulates all platform-specific code
• GetPennyWiseDataDir returns the correct path for any platform
• Auto-start uses Registry on Windows, .desktop file on Linux
• OpenURL launches the help page in the default browser