versioned_docs/version-1.1.0/guide/cpp/configuration.md

---
title: Configuration
sidebar_position: 4
id: configuration
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  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
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---

This page covers C++ runtime configuration. `Fory::builder()` creates xlang
payloads by default, and omitted compatible mode resolves to compatible mode in
xlang. Native mode is selected explicitly with `.xlang(false)` and defaults to
schema-consistent payloads.

## Builder Pattern

Use `Fory::builder()` to construct Fory instances with custom configuration:

```cpp
#include "fory/serialization/fory.h"

using namespace fory::serialization;

// Xlang mode with compatible schema evolution.
auto fory = Fory::builder().xlang(true).build();

// Schema-consistent xlang payloads.
auto fory = Fory::builder()
    .xlang(true)
    .compatible(false)
    .build();

// Native mode for C++-only traffic.
auto fory = Fory::builder()
    .xlang(false)
    .build();

// Native mode with compatible schema evolution.
auto fory = Fory::builder()
    .xlang(false)
    .track_ref(true)
    .max_dyn_depth(10)
    .compatible(true)
    .build();
```

## Configuration

### xlang(bool)

Select the wire mode.

```cpp
auto fory = Fory::builder()
    .xlang(false)
    .build();
```

When `true`, C++ writes the xlang wire format used by Java, Python, Go, Rust,
JavaScript/TypeScript, C#, Swift, Dart, Scala, and Kotlin. When `false`, C++
writes native-mode payloads for C++-only traffic.

**Default:** `true`

### compatible(bool)

Enable compatible schema evolution.

```cpp
auto fory = Fory::builder()
    .xlang(true)
    .compatible(true)
    .build();
```

When enabled, supports reading data serialized with different schema versions.
When omitted, xlang mode defaults to compatible mode. Native mode defaults to
schema-consistent mode and uses compatible mode only when this option is set.

**Default:** `true` in xlang mode; `false` in native mode

### track_ref(bool)

Enable/disable reference tracking for shared and circular references.

```cpp
auto fory = Fory::builder()
    .xlang(true)
    .track_ref(true)  // Enable reference tracking
    .build();
```

When enabled, avoids duplicating shared objects and handles cycles.

**Default:** `true`

### max_dyn_depth(uint32_t)

Set maximum allowed nesting depth for dynamically-typed objects.

```cpp
auto fory = Fory::builder()
    .xlang(true)
    .max_dyn_depth(10)  // Allow up to 10 levels
    .build();
```

This limits the maximum depth for nested polymorphic object serialization (e.g., `shared_ptr<Base>`, `unique_ptr<Base>`). This prevents stack overflow from deeply nested structures in dynamic serialization scenarios.

**Default:** `5`

**When to adjust:**

- **Increase**: For legitimate deeply nested data structures
- **Decrease**: For stricter security requirements or shallow data structures

### check_struct_version(bool)

Enable/disable struct version checking.

```cpp
auto fory = Fory::builder()
    .xlang(true)
    .compatible(false)
    .check_struct_version(true)  // Enable version checking
    .build();
```

When enabled, validates type hashes to detect schema mismatches.

**Default:** `false`

## Thread-Safe vs Single-Threaded

### Single-Threaded (Fastest)

```cpp
auto fory = Fory::builder().xlang(true).build();  // Returns Fory
```

Single-threaded `Fory` is the fastest option, but NOT thread-safe. Use one instance per thread.

### Thread-Safe

```cpp
auto fory = Fory::builder().xlang(true).build_thread_safe();  // Returns ThreadSafeFory
```

`ThreadSafeFory` uses a pool of Fory instances to provide thread-safe serialization. Slightly slower due to pool overhead, but safe to use from multiple threads concurrently.

## Configuration Summary

| Option                       | Description                             | Default                        |
| ---------------------------- | --------------------------------------- | ------------------------------ |
| `xlang(bool)`                | Use xlang mode                          | `true`                         |
| `compatible(bool)`           | Enable schema evolution                 | xlang: `true`; native: `false` |
| `track_ref(bool)`            | Enable reference tracking               | `true`                         |
| `max_dyn_depth(uint32_t)`    | Maximum nesting depth for dynamic types | `5`                            |
| `check_struct_version(bool)` | Enable struct version checking          | `false`                        |

## Security

Security-related configuration:

- Register all structs and polymorphic implementations before deserializing untrusted payloads.
- Use `check_struct_version(true)` with `compatible(false)` when exact schema matching is required.
- Keep `max_dyn_depth(...)` as low as your model permits to reject unexpectedly deep polymorphic
  graphs.
- Prefer concrete fields over broad polymorphic fields for untrusted input.

## Related Topics

- [Basic Serialization](basic-serialization.md) - Using configured Fory
- [Xlang Serialization](xlang-serialization.md) - xlang mode details
- [Type Registration](type-registration.md) - Registering types