Question

如何编译和安装libevent

Answer 1

#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。