【ZMQ】第一个C服务器
技术背景
ØMQ （也拼写作ZeroMQ，0MQ或ZMQ)，号称号称是“史上最快的消息队列”，基于c语言开发。ZMQ(以下ZeroMQ简称ZMQ)是一个简单好用的传输层，像框架一样的一个socket library，他使得Socket编程更加简单、简洁和性能更高。是一个消息处理队列库，可在多个线程、内核和主机盒之间弹性伸缩。
作为C开发人员有两个选择 CZMQ 或 libzmq （低级zeromq库）。
在这里简单记录 CentOS 下从零安装ZMQ相关依赖、解决各种问题最终实现一个最简单的请求-应答服务器-客户端效果。
ZeroMQ 在 centos下的安装
1）下载ZeroMQ
执行命令：
wget http://download.zeromq.org/zeromq-4.0.4.tar.gz
2）解压ZeroMQ
$ tar zvxf zeromq-4.0.4.tar.gz
$ mv zeromq-4.0.4 zeromq
$ cd zeromq
3）安装依赖
$ yum install libtool
$ ./autogen.sh
4）编译安装
$ ./configure
......
checking for gcc... no
checking for cc... no
checking for cl.exe... no
configure: error: in `/home/chuser/zeromq':
configure: error: no acceptable C compiler found in $PATH
See `config.log' for more details
提示缺少C编译器，先安装GCC。
$ sudo yum install gcc
安装OK！再次执行
$ ./configure
......
checking whether the C++ compiler works... no
configure: error: Unable to find a working C++ compiler
提示缺少C++编译器，先安装G++。
$ sudo yum install gcc-c++
安装OK！再次执行
$ ./configure
$ make
$ sudo make install
ZeroMQ安装成功！
libzmq 在 CentOS 下的安装
libzmq开源仓库： https://github.com/zeromq/libzmq
# 对于 CentOS 8，请以根用户 root 运行下面命令：
cd /etc/yum.repos.d/
wget https://download.opensuse.org/repositories/network:messaging:zeromq:release-stable/CentOS_8/network:messaging:zeromq:release-stable.repo
yum install zeromq-devel
# 对于 CentOS 7，请以根用户 root 运行下面命令：
cd /etc/yum.repos.d/
wget https://download.opensuse.org/repositories/network:messaging:zeromq:release-stable/CentOS_7/network:messaging:zeromq:release-stable.repo
yum install zeromq-devel
# 对于 CentOS 6，请以根用户 root 运行下面命令：
cd /etc/yum.repos.d/
wget https://download.opensuse.org/repositories/network:messaging:zeromq:release-stable/CentOS_6/network:messaging:zeromq:release-stable.repo
yum install zeromq-devel
Demo
(来源:https://zeromq.org/languages/c/#libzmq)
Server:
#include <zmq.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>
int main (void)
{
// Socket to talk to clients
void *context = zmq_ctx_new ();
void *responder = zmq_socket (context, ZMQ_REP);
int rc = zmq_bind (responder, "tcp://*:5555");
assert (rc == 0);
while (1) {
char buffer [10];
zmq_recv (responder, buffer, 10, 0);
printf ("Received Hello\n");
sleep (1); // Do some 'work'
zmq_send (responder, "World", 5, 0);
}
return 0;
}
Client:
Copy
#include <zmq.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
int main (void)
{
printf ("Connecting to hello world server…\n");
void *context = zmq_ctx_new ();
void *requester = zmq_socket (context, ZMQ_REQ);
zmq_connect (requester, "tcp://localhost:5555");
int request_nbr;
for (request_nbr = 0; request_nbr != 10; request_nbr++) {
char buffer [10];
printf ("Sending Hello %d…\n", request_nbr);
zmq_send (requester, "Hello", 5, 0);
zmq_recv (requester, buffer, 10, 0);
printf ("Received World %d\n", request_nbr);
}
zmq_close (requester);
zmq_ctx_destroy (context);
return 0;
}
将文件存入以libzmq_server.c，libzmq_client.c命名的文件。
运行下列命令编译：
gcc libzmq_server.c -o libzmq_server -lzmq
gcc libzmq_client.c -o libzmq_client -lzmq
若出现错误，请移步异常问题记录区寻找答案
分别在两个终端运行，若成功，效果如下：
$ ./libzmq_server
Received Hello
Received Hello
Received Hello
Received Hello
Received Hello
Received Hello
Received Hello
Received Hello
Received Hello
Received Hello
$ ./libzmq_client
Connecting to hello world server…
Sending Hello 0…
Received World 0
Sending Hello 1…
Received World 1
Sending Hello 2…
Received World 2
Sending Hello 3…
Received World 3
Sending Hello 4…
Received World 4
Sending Hello 5…
Received World 5
Sending Hello 6…
Received World 6
Sending Hello 7…
Received World 7
Sending Hello 8…
Received World 8
Sending Hello 9…
Received World 9
异常记录
undefined reference to `zmq_sendmsg'
解决方案:
编译时带上 -lzmq
例如：gcc -o hello hello.c -lzmq
error while loading shared libraries: libzmq.so.3
方法1：
找一下动态文件安装到哪里了：
$ whereis libzmq.so.3
$ find / -name libzmq.so.3
将 /usr/local/lib 加到共享库配置文件 /etc/ld.so.conf 中，该方法一劳永逸，但是需要有操作权限
# cat /etc/ld.so.conf
include ld.so.conf.d/*.conf
# echo "/usr/local/lib">>/etc/ld.so.conf
# ldconfig
再执行成功.
方法2：设置环境变量LDLIBRARYPATH，适合没有操作权限时使用
# vi ~/.bash_profile
编辑你当前用户的用户目录下的.bash_profile文件 在文件后面加上：
export LD_LIBRARY_PATH=/usr/local/lib/:$LD_LIBRARY_PATH
保存并关闭文件
# source ~/.bash_profile
使该文件改动生效（每次登录该用户时也会自动加载该文件，使文件生效） 执行成功
C程序头文件引用问题
一直没有搞清楚头文件引用 "" 和 <> 的区别，今天偶然查到：
- first：include<fileName.h> 引用系统头文件一般用<>。
- second：include"fileName.h" 引用自己定义的头文件一般用" "。
区别是<>首先去系统中去找，" "则在自己当前文件夹找。
一般情况下系统头文件在 usr/include/中。