Notes for Java and c Communication

1. little_endian

The web-based testing software consists of the C ++ data collection server program and the client Java display program. The former uses C ++ and the latter uses the Java language, and there is a data migration problem. Because
In a computer system, when a binary file containing numbers is moved from one structure to another, a large tail or a small tail problem occurs. There are two methods for storing different CPUs in multiple-node storage (such as four-byte INT ):
The method is called little_endian. The low bytes of data are placed at the top of the continuous storage area. The other method is big_endian.
The first place in the continued storage zone. The Intel 80*86 family processor is the last one that still sticks to the primary structure of tail. All other CPU Structures (Motorola
680 × 0 and all of them.) It is either a pure large tail or an adaptation to both the big tail and the small tail. The big tail is considered to be a more logical method ). When a number is written to a file by a tail processor
When the processor reads (or reverses) the number, it will be messed up (except 0 and-1 ).

Currently, in the project I participated in, the GM of the platform Center
Server is implemented in C language, while GM on our side
The client is implemented in Java. It is necessary to consider the large and small tail conversions during communication, mainly involving short, Int, long, string, and byte types.
Change.

2. Type bytes size issues

The basic types of C language are as follows:

 

Type	Definition	Description
Byte	Typedef Unsigned char byte	Single byte
Word	Typedef Unsigned short word	Double-byte unsigned integer
Sword	Typedef Signed short sword	Double-byte signed integer
DWORD	Typedef Unsigned int DWORD	Four-byte unsigned integer
Sdword	Typedef Signed int sdword	Four-byte signed integer

 

The eight basic data types of Java are as follows:

Byte 1 byte
Short
2 bytes
Int 4 bytes

Long
8 bytes (4 bytes in C)
2 bytes of char (1 byte in C)
Float
4 bytes
Double 8 bytes
Boolean bool;
False/true

 

3. Integration:

Examples of big tail and Small Tail conversion:

For example, there is an int of the Java type in hexadecimal notation.

00 00 80 01 (large tail)

To convert to C:

01 80 00 00 (Small Tail)

For example, the Short Type

40 02 (large tail)

02 40 (Small Tail)

For example, the Mina Communication Framework provides ready-made APIs for big-tail conversion.

Iobuffer. Order (byteorder.Little_endian
) // Converted to a small tail

Iobuffer. Order (byteorder.Big_endian
) // Converts it to a big tail

You can use byte [] to flip an array.
Arrayutils. Reverse (byte [])

To complete the conversion.

References:

Research on Real-time Data Migration of Java and C/C ++ programs