C ++客户端到Java服务器（TCP / IP） [英] C++ Client to a Java Server(TCP/IP)
问题描述
一开始，我是非常新的与sockects和TCP / IP数据包的网络，如果你能以一个非常清楚的方式解释，我会很感激。我的机器人程序第一次尝试使用kinect与我们当前的机器人，但我们有一个问题。目前他们在java中编码，而他们计划在C ++编码kinect。是否可以使用TCP / IP数据包在两种语言之间发送信息？我们需要一个C ++客户端和一个Java服务器。
To start off, i'm very new to networking with sockects and TCP/IP packets, i would appreciate it if you could explain in a very clear manner. My robotics program is attempting to use a kinect with our current robot for the first time, but we have a problem. Currently they code in java, while they plan on coding the kinect in C++. Is it possible to use TCP/IP packets to send information between the two languages? We need a C++ Client and a Java server. If anyone has links or examples i would really appreciate it, thanks!
推荐答案
Java和C / C ++之间沟通的真正问题是字节排序问题。如果要发送二进制数据，则必须清楚和完整地设计通信结构，包括数字大小（字节），位顺序（lsb / msb，交换字节或非交换字节，短整型，整型和longs）和结构包装（结构中字段之间的填充字节数）。
The real problems communicating between Java and C/C++ is the byte ordering problem. If you are going to be sending binary data, you must design the communications structures clearly and completely, including number sizes (in bytes), bit-order (lsb/msb, swapped-byte or non-swapped bytes in short, ints, and longs), and structure packing (the number of pad bytes between fields in a structure).
我建议你不要以二进制通信，如果你可以避免它。有两个原因：
I recommend that you don't communicate in binary if you can avoid it. For two reasons;
- 不必担心位顺序，字节交换和结构打包。
- 通信无需解码数据。
EDIT
在C / C ++中，数据以使CPU访问快速和容易的方式存储。类/结构的字段在字边界上对齐（因为大多数CPU只能以全字块的方式访问存储器），并且这些位被排序以匹配CPU。但是，CPU可以具有不同的位顺序和字大小（16,32,64，...）。大多数英特尔CPU都是小端，大多数其他设计都是大端。为了使生活更有趣，java虚拟机在每个平台上都是大端。 http://en.wikipedia.org/wiki/Endianness
所以，如果你想要两个C / C ++机器能够通信，那么你必须以一种可以读取它的方式发送数据。通常，为了在异质环境中通信（称为通过电线），您指定所有通信都以特定格式完成。 TCP / IP使用MSB（最高有效位）排序。
So, if you want two C/C++ machines to be able to communicate, then you must send the data in a way that both can read it. Normally, to communicate in a heterogenous environment (called 'over the wire') you specify that all communications are done in a particular format. TCP/IP uses MSB (most significant bit) ordering. All the programs then have to translate (if necessary) from the wire format.
因为CPU消耗字长块中的内存，所以编译器把pad字节放在字段之间不填满整个字。对于读取32位字的机器，这样的结构：
Because CPUs consume memory in word length chunks, then the compilers put pad bytes between fields that don't fill a whole machine word. For a machine that reads 32 bit words, a structure like this:
struct example1 {
char someFlag;
int someCount;
};
实际上需要8个字节的内存。第一字段由单个字节的数据和3个填充字节组成，使得整数引用在字边界上对齐。如果一个简单的通信器尝试发送这个结构中的数据，例如 send（& example1，sizeof（example1））; 到具有不同字大小或字节排序的另一个系统，其中另一个系统 read（& example1，sizeof（example1））; ，那么example1.someCount的值可能与预期非常不同。
would actually take 8 bytes of memory. The first field consists of a single byte of data and 3 pad bytes, so that the integer references are aligned on word boundaries. If a naive communicator tries to send the data in this structure, say send(&example1, sizeof(example1)); to another system with a different word size or byte ordering, where the other system does read(&example1, sizeof(example1));, then the value of example1.someCount may be very different than expected.
大多数通常是学术的，直到你把Java引入它。因为Java总是MSB格式。因此，即使在同一个硬件上，从C / C ++应用程序发送到Java应用程序也可能导致同样的意外结果。
Most of this is normally academic until you throw Java into it. Because Java is always MSB format. So sending from a C/C++ application to a Java application, even on the same hardware, may cause this same unexpected result.
Java包含我最喜欢的I / java.nio.ByteBuffer 。它有能力从几乎任何来源读int，longs，浮动和双打。如果你知道数据是如何创建的，这将读取它。 ByteBuffer有 getShort ， getInt 等方法获取任何类型，以及 order（）方法设置数据的字节顺序。
Java contains my favorite I/O class, java.nio.ByteBuffer. It has the ability to read ints, longs, floats, and doubles from practically any source. If you know how the data was created, this will read it. ByteBuffer has getShort, getInt, etc. methods to get any type, as well as an order() method to set the byte order of the data.
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