網路通訊常用的有2種：文字通訊和二進位制通訊。文章分別在兩種方式上實現erlang與c++通訊。

一、erlang 與 c++ 行通訊

行通訊是一種文字通訊，格式如“cmd args\n”，比較簡單，erlang接收資料也比較簡單，可以設定引數 {packet, line} ，缺點是表示方式單一，很難表示結構資料。

1、erlang 程式碼（server.erl）：

-module(server).
-export([start/0]).
-define( PORT, 5678).

%% 啟動服務並接受客戶端的連線
start() ->
  {ok, LSock} = gen_tcp:listen(?PORT, [binary, {packet, line},{active, false}]),
  io:format("socket listen: ~p on ~p ~n",[LSock, ?PORT]),
  accept(LSock).

accept(LSock) ->
  {ok, ASock} = gen_tcp:accept(LSock),
  spawn(fun() -> server_loop(ASock) end),
  accept(LSock).

server_loop(ASock) ->
  case gen_tcp:recv(ASock, 0) of
    {ok, Data} ->
      io:format("recv line data: ~p~n", [Data]),
      gen_tcp:send(ASock, Data),
      server_loop(ASock);
    {error, _} ->
      {ok, recv_error}
    end.
 

2、c++ 程式碼（test.cpp）：

#include <winsock2.h>
#include <iostream>
#pragma comment(lib, "ws2_32.lib")

int main(int argc, char* argv[])
{
	WSADATA wsaData;
	WSAStartup( MAKEWORD( 2, 2 ), &wsaData ); 
	SOCKET sc = WSASocket(AF_INET, SOCK_STREAM, 0, NULL, 0, NULL);
	SOCKADDR_IN addr;
	int len=sizeof(addr);
	addr.sin_family=AF_INET;
	addr.sin_addr.s_addr = inet_addr("127.0.0.1");
	addr.sin_port = htons(5678);
	connect(sc, (struct sockaddr *)&addr, len);
	char buff[1024];
	memset(buff, 0, 1024);

	char data[] = "aaaaaa\n";

	//傳送資料
	printf("send data: %s \n", data);
	send(sc, data, sizeof(data), 0);

	//接收資料
	recv(sc, buff, 1024, 0);
	printf("recv data: %s \n", buff);

	closesocket(sc);
	WSACleanup();
	getchar();
	return 0;
}
 

包體通訊是二進位制通訊，目前主要有結構體，json，asn.1，protobuf等等，最簡單還可以這樣定義：2個位元組cmd + 2個位元組字元長度 + 字元內容。

下面以結構體包體通訊示例：

1、erlang程式碼（server.erl）：

-module(server).
-export([start/0]).

-define( UINT, 32/unsigned-little-integer).
-define( INT, 32/signed-little-integer).
-define( USHORT, 16/unsigned-little-integer).
-define( SHORT, 16/signed-little-integer).
-define( UBYTE, 8/unsigned-little-integer).
-define( BYTE, 8/signed-little-integer).

-define( PORT, 5678).

%% 啟動服務並接受客戶端的連線
start() ->
  {ok, LSock} = gen_tcp:listen(?PORT, [binary, {packet, 0},{active, false}]),
  io:format("socket listen: ~p on ~p ~n",[LSock, ?PORT]),
  accept(LSock).

accept(LSock) ->
  {ok, ASock} = gen_tcp:accept(LSock),
  spawn(fun() -> server_loop(ASock) end),
  accept(LSock).

server_loop(ASock) ->
  case gen_tcp:recv(ASock, 0) of
    {ok, <<Len:?USHORT,Cmd:?USHORT,Contain:4/binary-unit:8,_Rest/binary>> = A} ->
      %% _Rest 匹配C++字串後面的結束符/0
      io:format("recv data: ~p ~p ~p~n", [Len, Cmd, Contain]),
      gen_tcp:send(ASock, A),
      server_loop(ASock);
    {ok, Data} ->
      io:format("recv unformated data: ~p~n", [Data]),
      server_loop(ASock);
    {error, _} ->
      {ok, recv_error}
    end.
 

#include <winsock2.h>
#include <iostream>
#pragma comment(lib, "ws2_32.lib")

struct data{
	unsigned short int len;
	unsigned short int cmd;
	char content[5] ;
};

int main(int argc, char* argv[])
{
	WSADATA wsaData;
	WSAStartup( MAKEWORD( 2, 2 ), &wsaData ); 
	SOCKET sc = WSASocket(AF_INET, SOCK_STREAM, 0, NULL, 0, NULL);
	SOCKADDR_IN addr;
	int len=sizeof(addr);
	addr.sin_family=AF_INET;
	addr.sin_addr.s_addr = inet_addr("127.0.0.1");
	addr.sin_port = htons(5678);
	connect(sc, (struct sockaddr *)&addr, len);
	char buff[1024];
	memset(buff, 0, 1024);

	struct data pdata = {4, 1001, "test"};

	//傳送資料
	printf("send data: %d %d %s \n", pdata.len, pdata.cmd, pdata.content);
	send(sc, (char *)&pdata, sizeof(pdata), 0);

	//接收資料
	recv(sc, buff, 1024, 0);
	struct data * pdata_get = (struct data *) buff;
	printf("recv data: %d %s \n", pdata_get->cmd, pdata_get->content);

	closesocket(sc);
	WSACleanup();
	getchar();
	return 0;
}