libevent实践01：准备源码、搭建项目、编译脚本和入门例子

编译源码

libevent是一个Reactor事件库。

我的理解，就是封装了select、epoll、poll的函数库。有使用select，poll，epoll的需求就可以使用的。

官网地址：https://libevent.org/

下载源码：

https://github.com/libevent/libevent/releases/download/release-2.1.12-stable/libevent-2.1.12-stable.tar.gz

下载后解压源码：

tar zxvf libevent-2.1.12-stable.tar.gz

 在源码目录下创建_install目录，然后执行 ./configure --prefix=/big/libevent/libevent-2.1.12-stable/_install。

/big/libevent/libevent-2.1.12-stable/_install这个就是编译后安装的目录。详细步骤如下所示：

lkmao@ubuntu:/big/libevent$ ls
libevent-2.1.12-stable  libevent-2.1.12-stable.tar.gz
lkmao@ubuntu:/big/libevent$ cd libevent-2.1.12-stable/
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable$ mkdir _install
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable$ cd _install/
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable/_install$ pwd
/big/libevent/libevent-2.1.12-stable/_install
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable/_install$ cd ..
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable$ ./configure --prefix=/big/libevent/libevent-2.1.12-stable/_install

        这一步是用来生成编译时用的makefile文件，其中，--prefix用来指定Libevent的安装目录。输入make进行编译，成功后再输入make install，然后就可以看到/big/libevent/libevent-2.1.12-stable/_install下面已经有文件生成了：

lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable$ make
/*略*/
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable$ make install
/*略*/
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable$ cd _install/
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable/_install$ ls
bin  include  lib

        其中include是存放头文件的目录，lib是存放动态库和静态库的目录。接下来用一个小程序来测试是否工作正常。

二 创建项目并测试 

 创建一个目录，用于存放我们的工程文件和源码：

lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable/_install$ mkdir learn
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable/_install$ cd learn/

在目录下创建三个文件，

1. 编译脚本build.sh
2. cmake文件CMakeLists.txt
3. 源码文件main_01.c 

lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable/_install/learn$ ls
build.sh  CMakeLists.txt  main_01.c
lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable/_install/learn$

 下面分别介绍三个文件内容

main_01.c

创建源文件：main_01.c,输入如下代码，如果写过select函数，很快就能了解，此代码的功能是设置一个定时器，然后每隔1秒就打印一次“timer wakeup!counter = %d”。

 printf("timer wakeup!counter = %d\n",counter++);

#include 
#include 
#include 
#include 
struct event ev;
struct timeval tv;void time_cb(int fd, short event, void *argc)
{
static int counter = 0;printf("timer wakeup!counter = %d\n",counter++);event_add(&ev, &tv);
}int main()
{struct event_base *base = event_init();tv.tv_sec = 1;tv.tv_usec = 0;evtimer_set(&ev, time_cb, NULL);event_base_set(base, &ev);event_add(&ev, &tv);event_base_dispatch(base);
}

build.sh

#!/bin/bash
set -e
rm -rf _build_
mkdir _build_ -p
cmake -S ./ -B _build_
make -C _build_
./_build_/main_01

要保证build.sh文件是可执行的

chmod 777 build.sh 

CMakeLists.txt

project(libevent_project)
cmake_minimum_required(VERSION 3.8)message(STATUS "lkmao:CMAKE_SOURCE_DIR -- ${CMAKE_SOURCE_DIR}")set(LIBEVET_INSTALL_PATH "/big/libevent/libevent-2.1.12-stable/_install/")
include_directories(${LIBEVET_INSTALL_PATH}/include 
)# set(CMAKE_C_COMPILER /arm-gcc/bin/arm-linux-gnueabihf-gcc)
# set(CMAKE_CXX_COMPILER /arm-gcc/bin/arm-linux-gnueabihf-g++)# SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99 -pthread")
SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -pthread")
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -pthread -lstdc++")message(STATUS "lkmao:PROJECT_SOURCE_DIR -- ${PROJECT_SOURCE_DIR}")add_executable(main_01 main_01.c)
target_link_libraries(main_01 ${LIBEVET_INSTALL_PATH}/lib/libevent.so)

测试验证

文件都准备好，并输入内容后执行build.sh文件，执行结果如下所示：

lkmao@ubuntu:/big/libevent/libevent-2.1.12-stable/_install/learn$ ./build.sh 
-- The C compiler identification is GNU 5.4.0
-- The CXX compiler identification is GNU 5.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- lkmao:CMAKE_SOURCE_DIR -- /big/libevent/libevent-2.1.12-stable/_install/learn
-- lkmao:PROJECT_SOURCE_DIR -- /big/libevent/libevent-2.1.12-stable/_install/learn
-- Configuring done
-- Generating done
-- Build files have been written to: /big/libevent/libevent-2.1.12-stable/_install/learn/_build_
make: Entering directory '/big/libevent/libevent-2.1.12-stable/_install/learn/_build_'
make[1]: Entering directory '/big/libevent/libevent-2.1.12-stable/_install/learn/_build_'
make[2]: Entering directory '/big/libevent/libevent-2.1.12-stable/_install/learn/_build_'
Scanning dependencies of target main_01
make[2]: Leaving directory '/big/libevent/libevent-2.1.12-stable/_install/learn/_build_'
make[2]: Entering directory '/big/libevent/libevent-2.1.12-stable/_install/learn/_build_'
[ 50%] Building C object CMakeFiles/main_01.dir/main_01.c.o
[100%] Linking C executable main_01
make[2]: Leaving directory '/big/libevent/libevent-2.1.12-stable/_install/learn/_build_'
[100%] Built target main_01
make[1]: Leaving directory '/big/libevent/libevent-2.1.12-stable/_install/learn/_build_'
make: Leaving directory '/big/libevent/libevent-2.1.12-stable/_install/learn/_build_'
timer wakeup!counter = 0
timer wakeup!counter = 1
timer wakeup!counter = 2
timer wakeup!counter = 3
timer wakeup!counter = 4
timer wakeup!counter = 5
timer wakeup!counter = 6

由下面的截图可知，我们的测试代码开始运行了。

四 命令行编译 

gcc main_01.c -o testEvent -I /big/libevent/libevent-2.1.12-stable/_install/include/ -L /big/libevent/libevent-2.1.12-stable/_install/lib/ -levent

使用命令行，需要设置环境变量，要不然，找不到库。 

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