?如何编译和安装libevent

编译和安装步骤：

$ apt-get install git
$ git clone https://github.com/libevent/libevent.git
$ cd libevent
$ apt-get install cmake
$ apt-get install libssl-dev
$ mkdir build && cd build
$ cmake .. # Default to Unix Makefiles.
$ make
$ make verify # (optional)
$ make install

一些学习文档：

Fast portable non-blocking network programming with Libevent: http://www.wangafu.net/~nickm/libevent-book/
libevent-examples: https://github.com/jasonish/libevent-examples
multi-thread libevent: https://sourceforge.net/projects/libevent-thread/

针对第一个例子：

http://www.wangafu.net/~nickm/libevent-book/Ref1_libsetup.html
le.c内容：

#include <event2/event.h>
#include <stdio.h>

#define EVENT_LOG_DEBUG 0
#define EVENT_LOG_MSG   1
#define EVENT_LOG_WARN  2
#define EVENT_LOG_ERR   3

/* Deprecated; see note at the end of this section */
#define _EVENT_LOG_DEBUG EVENT_LOG_DEBUG
#define _EVENT_LOG_MSG   EVENT_LOG_MSG
#define _EVENT_LOG_WARN  EVENT_LOG_WARN
#define _EVENT_LOG_ERR   EVENT_LOG_ERR

typedef void (*event_log_cb)(int severity, const char *msg);

void event_set_log_callback(event_log_cb cb);

static void discard_cb(int severity, const char *msg)
{
    /* This callback does nothing. */
}

static FILE *logfile = NULL;
static void write_to_file_cb(int severity, const char *msg)
{
    const char *s;
    if (!logfile)
        return;
    switch (severity) {
        case _EVENT_LOG_DEBUG: s = "debug"; break;
        case _EVENT_LOG_MSG:   s = "msg";   break;
        case _EVENT_LOG_WARN:  s = "warn";  break;
        case _EVENT_LOG_ERR:   s = "error"; break;
        default:               s = "?";     break; /* never reached */
    }
    fprintf(logfile, "[%s] %s\n", s, msg);
}

/* Turn off all logging from Libevent. */
void suppress_logging(void)
{
    event_set_log_callback(discard_cb);
}

/* Redirect all Libevent log messages to the C stdio file ‘f‘. */
void set_logfile(FILE *f)
{
    logfile = f;
    event_set_log_callback(write_to_file_cb);
}
int main(int argc, char **argv)
{
FILE *fp=fopen("/tmp/test.txt", "w+");
set_logfile(fp);
fclose(fp);
return 0;
}

$ gcc le.c -o le -levent
$ ./le
没有输出任何文本到/tmp/test.txt，因为main函数中没有调用log，当然文中建议我们不要直接使用用户提供的event_log_cb回调函数，因为这样做是不安全的。
有人翻译了这本文档，可以参考下：
http://popozhu.github.io/page/7/
http://popozhu.github.io/page/6/

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