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Converting C++ Unsigned Numbers to Java
Dealing with unsigned values from C++ can seem like a headache sometimes, if you don't understand what's going on "under the hood". Luckily you don't have to understand everything under the hood to read a binary file written by a C++ app in Java or vice versa, just have a vague understanding of the issues involved..
The major differences that can cause challenges are: 1) Figuring out which data types are "equivalent" 2) Java doesn't have unsigned types, but C++ types can be signed or unsigned. 3) Some types just don't have a direct equivalent (eg: C++ float has no exact match in Java)
Here's a table showing how internally C++ (on a 32-bit version of Windows) and Java store integer types:
Size
1 byte
2 bytes
4 bytes
8 bytes
16 bytes
8 bits
16 bits
32 bits
64 bits
128 bits
C++ (on Win32)
byte
short
int/long
long long
__int128
Java
byte
short
int
long
BigInteger
If you are using a 64 bit operating system or a 16 bit operating system, the C++ sizes such as how many bytes an int is will vary. Microsoft invented some funky looking type names like __int32 for those times when you want to tell the compiler "when I said I wanted 4 bytes for my integer, I meant 4 bytes", but that may only work with Microsoft compilers.
Here are some other binary data types that are frequently encountered:
Size
1 byte
2 bytes
4 bytes
8 bytes
16 bytes
8 bits
16 bits
32 bits
64 bits
128 bits
C++ (on Win32)
char/bool
 
float
double/long double
 
Java
boolean
char
 
float
double
Going from C++ to Java:
C++ Type
Java Type
Read from File **
Then translate the value
unsigned byte
(signed) short byte a = in.readByte(); short b = (short)(a & 0xff);
unsigned short
(signed) int short a = in.readShort(); int b = a & 0xffff;
unsigned int/long
(signed) long int a = in.readInt(); long b = a & 0xffffffffL;
float*
float int a = in.readInt(); float b = Float.intBitsToFloat(a);
double
float float a = in.readFloat(); //doing nothing extra
*note: because Java does not have a 4 byte float, converting 4 byte c++ float to 8 byte java float and then back to 4 byte c++ float may result in rounding errors. Use Float.floatBitsToInt(floatValue); to convert in the other direction. ** in refers to a binary input stream type of your choice.
To convert back and forth, you just cast in the to C++ direction. Easy.
Code example: (int or short could be used here just as well)
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7 public static short toUnsigned( byte b) {      return ( short )(b & 0xff ); }
  public static byte toSigned( short i) {       return ( byte ) i; }
*C++ type sizes are assuming you are running a 32 bit version of Windows. You can always explicitly set your sizing by declaring the types as__int8 (unsigned__int8)
 
For a C++ unsigned byte (value 0 to 255), mask with 0xff and store the result in a short:
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2 byte a = inputStream.readByte(); short b = ( short )(a & 0xff );
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