---
description: Binary data conversion rules when reading C++ binary files in C#
---

# Binary Data Conversion Rules (C++ to C#)

When reading binary data from C++ files using `FileStream`, follow these conversion patterns based on the variable type in the original C++ struct.

## Important Type Mappings

- `unsigned long` in C++ → `uint` in C#
- `bool` in C++ → 1 byte (read as `byte` in C#, then convert with `> 0`)
- `wchar_t` on Windows → 2 bytes
- `task_char` → `ushort`
- Pointer size in C++ binary → typically 4 bytes (32-bit)

**Critical**: When reading binary data, match the original C++ memory layout exactly, accounting for struct packing and alignment.

## Case 1: Normal Value Type Variables (Primitives)

**Pattern**: Directly stored scalar values (no arrays, no pointers, no user-defined structs)

**C++ Examples**:
```cpp
unsigned long m_ID;
bool m_bHasSign;
int m_lAvailFrequency;
float m_fLibraryTasksProbability;
```

**C# Conversion**:
```csharp
// Read value and assign to the field
fixedData.m_ID = AAssit.ReadFromBinaryOf<uint>(fp, ref readBytes);

// Special case for bool: read as byte and compare with > 0
fixedData.m_bHasSign = AAssit.ReadFromBinaryOf<byte>(fp, ref readBytes) > 0;
fixedData.m_bChooseOne = AAssit.ReadFromBinaryOf<byte>(fp, ref readBytes) > 0;

// Other primitive types
fixedData.m_lAvailFrequency = AAssit.ReadFromBinaryOf<int>(fp, ref readBytes);
fixedData.m_fLibraryTasksProbability = AAssit.ReadFromBinaryOf<float>(fp, ref readBytes);
```

**Rule**: Use `AAssit.ReadFromBinaryOf<T>(fp, ref readBytes)` where T is the C# equivalent type.

**Important for bool**: C++ bool is stored as 1 byte in binary files. Always read as `byte` and convert to C# bool using `> 0`:
```csharp
// Correct pattern for bool
fixedData.m_boolField = AAssit.ReadFromBinaryOf<byte>(fp, ref readBytes) > 0;
```

---

## Case 2: Fixed-Size Arrays (Inline Memory)

**Pattern**: Arrays with a known constant size defined by a macro or constant

**C++ Examples**:
```cpp
task_char m_szName[MAX_TASK_NAME_LEN];          // MAX_TASK_NAME_LEN = 30
char m_tmType[MAX_TIMETABLE_SIZE];              // MAX_TIMETABLE_SIZE = 32
task_tm m_tmStart[MAX_TIMETABLE_SIZE];
task_tm m_tmEnd[MAX_TIMETABLE_SIZE];
```

**C# Conversion**:
```csharp
// Read array from binary and assign to the field
fixedData.m_szName = AAssit.ReadArrayFromBinary<ushort>(fp, TaskTemplConstants.MAX_TASK_NAME_LEN, ref readBytes);
fixedData.m_tmType = AAssit.ReadArrayFromBinary<byte>(fp, TaskTemplConstants.MAX_TIMETABLE_SIZE, ref readBytes);
fixedData.m_tmStart = AAssit.ReadArrayFromBinary<task_tm>(fp, TaskTemplConstants.MAX_TIMETABLE_SIZE, ref readBytes);
fixedData.m_tmEnd = AAssit.ReadArrayFromBinary<task_tm>(fp, TaskTemplConstants.MAX_TIMETABLE_SIZE, ref readBytes);
```

**Rule**: Use `AAssit.ReadArrayFromBinary<T>(fp, arraySize, ref readBytes)` where:
- `T` is the C# equivalent element type
- `arraySize` is the predefined constant size

---

## Case 3: Pointer to User-Defined Type or String

**Pattern**: Fields that store only the pointer address, not the actual object/data

**C++ Examples**:
```cpp
task_char* m_pszSignature;
AWARD_DATA* m_Award_S;
Task_Region* m_pDelvRegion;
ITEM_WANTED* m_PremItems;
```

**C# Conversion**:
```csharp
// Skip pointer size (4 bytes for 32-bit pointers)
// The content is not inlined in the struct
fp.Seek(4, SeekOrigin.Current);
```

**Rule**: Skip 4 bytes using `fp.Seek(4, SeekOrigin.Current)` because only the pointer address is stored in the binary file, not the actual data.

**Note**: If the pointed-to data exists separately in the file, it must be read later based on additional logic (e.g., checking a count variable or flag).

---

## Case 4: User-Defined Struct (Inline, Not Pointer)

**Pattern**: A complete user-defined struct embedded directly in the parent struct

**C++ Examples**:
```cpp
task_tm m_tmAbsFailTime;      // Inline struct
AWARD_DATA m_Award_S;         // Inline struct (if not a pointer)
```

**C# Conversion**:
```csharp
// Skip the full size of the struct in bytes
// Check the struct's internal members and padding to calculate correct size
fp.Seek(24, SeekOrigin.Current);  // Example: sizeof(task_tm) = 24 bytes on Windows/MSVC
```

**Rule**: 
1. Calculate the exact size of the struct including padding
2. Skip that many bytes using `fp.Seek(structSize, SeekOrigin.Current)`

**Important**: Do not rely on hardcoded numbers. Calculate the actual struct size considering:
- Size of each member
- Struct packing (`Pack = 1`, `Pack = 4`, etc.)
- Platform-specific alignment rules

**Alternative**: If you need the data, read the struct directly:
```csharp
fixedData.m_tmAbsFailTime = AAssit.ReadFromBinaryOf<task_tm>(fp, ref readBytes);
```

---

## Case 5: Pointer to Basic Type (Not Inline)

**Pattern**: Pointer to a basic/primitive type where only the pointer address is stored in the struct. The pointed-to content (if any) is stored elsewhere in the file and must be read later based on counts/flags.

**C++ Examples**:
```cpp
ushort* m_pszSignature;     // Pointer to ushort
int* m_plChangeKey;         // Pointer to int
bool* m_pbChangeType;       // Pointer to bool
float* m_pFloatArray;       // Pointer to float
```

**C# Conversion**:
```csharp
// Always skip the pointer address (4 bytes in the binary layout)
fp.Seek(4, SeekOrigin.Current);
```

**Rule**: For any pointer (to basic or user-defined types), always skip 4 bytes to account for the stored pointer address in the C++ binary. The actual data, if present, should be read later using accompanying count/flag fields.

**Note**: This assumes the source binary was written with 32-bit pointer sizes. If you ever process binaries with 64-bit pointer sizes, adjust accordingly.

---

## Decision Tree

Use this flowchart to determine which case applies:

```
Is it a pointer (has * in C++)?
├── YES
│   ├── Is it a user-defined type (struct/class)?
│   │   ├── YES → Case 3: Skip 4 bytes (pointer address)
│   │   └── NO (basic type) → Case 5: Skip 4 bytes (pointer address)
│   └── NO
│       ├── Is it an array with predefined size?
│       │   ├── YES → Case 2: Read array using ReadArrayFromBinary
│       │   └── NO
│       │       ├── Is it a user-defined struct (inline)?
│       │       │   ├── YES → Case 4: Skip sizeof(struct) or read struct
│       │       │   └── NO → Case 1: Read value using ReadFromBinaryOf
```

---

## Common Patterns and Examples

### Pattern: Conditional Data Reading

When a field has associated data only if a flag/count is set:

**C++ Example**:
```cpp
bool m_bHasSign;
task_char* m_pszSignature;  // Only has data if m_bHasSign is true

unsigned long m_ulTimetable;
task_tm* m_tmStart;         // Only has data if m_ulTimetable > 0
```

**C# Conversion**:
```csharp
// First read the flag/count (read bool as byte and convert with > 0)
fixedData.m_bHasSign = AAssit.ReadFromBinaryOf<byte>(fp, ref readBytes) > 0;

// Skip the pointer (Case 3)
fp.Seek(4, SeekOrigin.Current);

// Later, conditionally read the actual data
if (fixedData.m_bHasSign)
{
    fixedData.m_pszSignature = AAssit.ReadArrayFromBinary<ushort>(fp, MAX_TASK_NAME_LEN, ref readBytes);
}
```

### Pattern: String Conversion

For `task_char` arrays (which are `ushort` arrays in C#):

```csharp
// Read the array
fixedData.m_szName = AAssit.ReadArrayFromBinary<ushort>(fp, MAX_TASK_NAME_LEN, ref readBytes);

// Convert to readable string
TaskTemplUtils.convert_txt(ref fixedData.m_szName, MAX_TASK_NAME_LEN, TaskTemplUtils.uint_to_ushort(fixedData.m_ID));
string taskName = ByteToStringUtils.UshortArrayToCP936String(fixedData.m_szName);
```

---

## Reference: AAssit Helper Methods

From [AAssit.cs](mdc:Assets/PerfectWorld/Scripts/Common/DataProcess/AAssit.cs):

```csharp
// Read a single value
public static T ReadFromBinaryOf<T>(FileStream fp, ref long readBytes) where T : struct

// Read an array of values
public static T[] ReadArrayFromBinary<T>(FileStream fp, int count, ref long readBytes) where T : struct
```

---

## Best Practices

1. **Always track readBytes**: Pass `ref readBytes` to track how many bytes have been read for debugging
2. **Match C++ layout exactly**: Ensure struct packing in C# matches C++ (`Pack = 1` is common)
3. **Document your assumptions**: Add comments explaining the byte sizes you're skipping
4. **Verify with logs**: Log read values to verify correctness
5. **Check file position**: Use `fp.Position` to verify you're reading from the expected location
6. **Handle platform differences**: Be aware of 32-bit vs 64-bit pointer sizes (though binary files usually use fixed sizes)

---

## Common Mistakes to Avoid

❌ **Wrong**: Reading bool directly as bool type
```csharp
// C++: bool m_bHasSign
fixedData.m_bHasSign = AAssit.ReadFromBinaryOf<bool>(fp, ref readBytes);  // Wrong!
```

✅ **Correct**:
```csharp
// Read as byte and compare with > 0
fixedData.m_bHasSign = AAssit.ReadFromBinaryOf<byte>(fp, ref readBytes) > 0;  // Correct!
```

---

❌ **Wrong**: Skipping only `sizeof(basic type)` for a pointer in Case 5
```csharp
// C++: ushort* m_pszSignature
fp.Seek(2, SeekOrigin.Current);  // Wrong! Do not skip sizeof(ushort) for pointers
```

✅ **Correct**:
```csharp
// Always skip the pointer address (4 bytes)
fp.Seek(4, SeekOrigin.Current);
```

---

❌ **Wrong**: Reading inline array as a single value
```csharp
// C++: char m_tmType[MAX_TIMETABLE_SIZE]
byte value = AAssit.ReadFromBinaryOf<byte>(fp, ref readBytes);  // Wrong!
```

✅ **Correct**:
```csharp
byte[] values = AAssit.ReadArrayFromBinary<byte>(fp, MAX_TIMETABLE_SIZE, ref readBytes);
```

---

❌ **Wrong**: Not accounting for struct padding
```csharp
// C++: struct with padding
fp.Seek(20, SeekOrigin.Current);  // Might be wrong due to padding!
```

✅ **Correct**:
```csharp
// Calculate actual size with padding
// Or read the struct directly if needed
fixedData.m_structField = AAssit.ReadFromBinaryOf<MyStruct>(fp, ref readBytes);
```