File format data types

From ModdingWiki

This is a list of all the data types used in the file format descriptions on the wiki. They are loosely based on common C/C++ data types, and should be used throughout the wiki for consistency.

Type list

Numeric values

Character strings

Misc data types

Big endian vs little endian

For numeric values larger than a single byte, the endianness specifies how the values are split over multiple bytes. For example a hex value of 0x1234AABB when written to a file will take up two bytes, as follows:

For those languages that allow direct memory access such as C/C++, converting an integer value to a byte array will reveal the value stored in-memory in the same order as the table above.

Normally when reading or writing a variable to a file a programmer will simply pass the memory address of the variable, resulting in the file mirroring the byte order in memory. This is no problem when reading the variable back in on the same system, as the byte order will match. However when reading data from a different system (for example using an Intel PC to read files from a PowerPC Mac) the byte order will be opposite to what the system expects and the programmer must convert the values manually.

Conversion examples

If a value is being read on the same system (little to little or big to big) then no action is required. If the systems are different, then the values must be swapped. The following sections list examples for different programming languages.

C/C++

// 16-bit
int in = 0x1234;
int out = ((in & 0xFF) << 8) | (in >> 8);
// out should now be 0x3412
 
// 32-bit
int in = 0x1234AABB;
int out =
  ((in & 0xFF) << 24) |
  ((in & 0xFF00) << 8) |
  ((in & 0xFF0000) >> 8) |
  (in >> 24);
// out should now be 0xBBAA3412

Visual Basic .NET

Function ByteSwap16(ByVal InValue as Int16) as Int16
  Return ((InValue And 255) << 8) Or (InValue >> 8)
End Function
 
Function ByteSwap32(ByVal InValue as Int32) as Int32
  Return ((InValue And &HFF) << 24) Or _
         ((InValue And &HFF00) << 8) Or _
         ((InValue And &HFF0000) >> 8) Or _
         (InValue >> 24)
End Function