Delphi to C++ Builder: Performance Tips and Code Translation Tricks

Modernizing Delphi Apps with C++ Builder: Tools, Strategies, and ExamplesModernizing legacy Delphi applications can extend their useful life, improve performance, and make them maintainable by teams more familiar with modern C++ toolchains. C++ Builder (part of Embarcadero RAD Studio) offers strong Windows GUI support, VCL compatibility, and a migration path that leverages existing Delphi code, components, and expertise. This article explains why you might modernize a Delphi app to C++ Builder, examines available tools, outlines strategies, and gives concrete examples and code patterns to guide the conversion.

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Why migrate Delphi apps to C++ Builder?

• Preserve investment in VCL/UI: Delphi apps commonly use the Visual Component Library (VCL). C++ Builder supports VCL and allows reuse of forms, components, and much UI code.
• Access to C++ ecosystem: Converting to C++ opens native access to modern C++ libraries, tooling, and performance characteristics.
• Team and hiring: Many organizations have C++ developers or want to standardize on C++ for interoperability with other systems.
• Performance and system integration: C++ can provide lower-level control for performance-critical parts and easier integration with C/C++ SDKs.
• Cross-language interoperability: Mixed-language projects (Delphi + C++) can combine strengths during staged migration.

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Tools you can use

• C++ Builder (RAD Studio) — primary IDE supporting VCL, FMX, and mixed-language projects.
• Embarcadero’s conversion utilities — project and header importers that help create C++ Builder projects from Delphi ones.
• Third-party tools and scripts — for specific code transformations (namespace, identifier, and type adjustments).
• Static analysis and refactoring tools — to identify Delphi-specific idioms and unsafe patterns needing attention.
• Version control (git) — enable branching for incremental migration and CI builds.
• Unit test frameworks — DUnit for Delphi, CppUnit or Catch2 for C++ parts; automated tests to ensure behavioral parity.

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Migration strategies

Choose a strategy based on project size, risk tolerance, and resources:

1. Incremental mixed-language approach (recommended for large projects)

   • Keep existing Delphi units and forms; create new modules in C++.
   • Use object pascal units compiled alongside C++ objects — C++ Builder supports linking to Delphi runtime units in many cases.
   • Gradually replace Delphi units with C++ equivalents.
   • Advantages: low risk, continuous delivery, reuse of UI and business logic.
   • Drawbacks: build complexity, mixed-language debugging.

2. Full rewrite in C++ (use for small codebases or when redesign is needed)

   • Reimplement core logic and UI using native C++ idioms and C++ Builder forms.
   • Advantages: clean design, modern C++ usage.
   • Drawbacks: high cost, greater risk of behavioral regressions.

3. Wrapper/shim strategy

   • Wrap Delphi modules behind a C API or COM interfaces; call them from C++ until replacement.
   • Useful when keeping a stable binary interface is required.

4. Component-by-component replacement

   • Replace or upgrade third-party components to C++-friendly equivalents while keeping application code more intact.

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Planning and preparation

• Inventory codebase: list units, forms, components, and third-party libs.
• Identify platform dependencies (Windows APIs, COM, database drivers).
• Create a test suite and baseline behavior metrics (performance, memory).
• Prepare build/CI that supports both Delphi and C++ Builder toolchains.
• Decide code style and naming conventions for the C++ side (avoid mixing Pascal-style identifiers if possible).

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Key technical considerations

• VCL and Forms
  • VCL is supported in C++ Builder; .dfm form files remain usable. You can include existing forms by adding the form units to the C++ project and letting the IDE generate wrapper headers.
• Data types & language differences
  • Delphi’s String maps to UnicodeString/UnicodeString in C++ Builder, but careful attention is needed for memory and ownership semantics.
  • Delphi sets, variants, and certain RTL classes have no direct C++ analogs — require wrappers or reimplementation.
• Exception handling
  • Delphi exceptions (Exception class) are supported, but mixing Delphi exceptions and C++ exceptions requires cautious boundaries.
• Memory and object ownership
  • Delphi uses TObject-based ownership patterns and automatic memory patterns (e.g., component ownership). Translate ownership semantics explicitly in C++ (smart pointers, RAII).
• Threading
  • Synchronize GUI updates using Synchronize/Queue in Delphi; in C++ use TThread::Synchronize/TThread::Queue or platform-native constructs.
• Packages and components
  • DCUs and BPLs: some Delphi binary units might not be directly usable; prefer source where possible.
• Third-party libraries
  • Evaluate availability of C++ Builder-compatible versions; if only Delphi sources exist, they may need conversion.

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Concrete examples and code patterns

Adding an existing Delphi form to a C++ Builder project

1. Add the .pas and .dfm files to your C++ Builder project.
2. The IDE generates a header (.hpp) that exposes the form class — you can include it in C++ source: “`cpp #include “MainForm.hpp”

void __fastcall TSomeOtherForm::OpenMainForm() {

auto form = new TMainForm(this); try {     form->ShowModal(); } __finally {     delete form; } 

}

Notes: - Use the IDE-generated header; it maps Delphi properties and events into C++ types. - Ownership: follow the VCL ownership model to avoid leaks. ### Translating a Delphi function to C++ Delphi: ```pascal function SumArray(const A: array of Integer): Integer; var i: Integer; begin   Result := 0;   for i := 0 to High(A) do     Result := Result + A[i]; end; 

C++:

int SumArray(const std::vector<int>& a) {     int result = 0;     for (int v : a) result += v;     return result; } 

Tips:

• Replace open-array parameters with std::vector or span for safety.
• Use algorithms (std::accumulate) when appropriate.

Handling Delphi strings and WideChar API

• Use UnicodeString (Embarcadero type) when interacting with VCL; convert to std::string/std::wstring only at boundaries. Example conversion:

  
  UnicodeString us = L"Hello"; std::wstring ws = us.c_str(); // narrow/wide conversion as needed 

Wrapping Delphi units with a C API

• Create a small Delphi DLL exposing plain C functions that call into Pascal code, then link/call from C++: Delphi side (exported): “`pascal library DelphiShim;

uses SysUtils, Classes;

function AddNumbers(a, b: Integer): Integer; stdcall; begin Result := a + b; end;

exports AddNumbers;

begin end.

C++ caller: ```cpp typedef int (__stdcall *TAdd)(int,int); HMODULE h = LoadLibrary(L"DelphiShim.dll"); auto Add = (TAdd)GetProcAddress(h, "AddNumbers"); int r = Add(2,3); FreeLibrary(h); 

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Testing and validation

• Unit tests: port/create tests for business logic; run them in CI.
• UI regression: take screenshots or automated UI tests where possible (TestComplete, Ranorex, or custom scripts).
• Performance benchmarks: compare memory and CPU before/after migration.
• Automated integration tests for database, web services, and file I/O.

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Examples of common pitfalls and fixes

• Strings and encoding: failing to convert between UTF-16/UTF-8 can cause corruption — centralize conversions.
• Ownership leaks: Delphi component ownership differs from typical C++ RAII; use std::unique_ptr or VCL ownership patterns carefully.
• Event wiring: C++ syntax for events differs; use the IDE to wire event handlers to avoid signature mismatches.
• Conditional compilation: Delphi code with platform-specific directives may need rework to compile under C++ Builder.

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When to stop migrating and keep Delphi

• If a module is stable, rarely changed, and has no dependency problems, keeping it in Delphi and interoperating with new C++ code can be pragmatic.
• If third-party components are only available as Delphi BPLs and replacement is costly, retain Delphi components and wrap them.

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Suggested migration checklist

• [ ] Inventory project files, components, and dependencies.
• [ ] Add automated tests and CI for current Delphi app.
• [ ] Create a mixed-language project template in C++ Builder.
• [ ] Port small, self-contained modules to C++ first.
• [ ] Verify UI functionality using existing .dfm forms.
• [ ] Replace or wrap third-party components as needed.
• [ ] Monitor performance and memory metrics.
• [ ] Remove Delphi dependencies gradually once C++ equivalents are stable.

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Final thoughts

Migrating Delphi applications to C++ Builder is often a pragmatic middle path: it preserves investment in VCL/UI while enabling modernization with C++. Use incremental migration, maintain comprehensive tests, and leverage the IDE’s mixed-language support to reduce risk. With careful planning you can modernize architecture, improve maintainability, and adopt modern C++ practices without discarding proven Delphi UI and business logic.