linux无法编译libevent，一直报错，但是我有装openssl

Question

执行完configure后make,报错：

make
make  all-recursive
make[1]: Entering directory `/libevent-2.0.21-stable'
Making all in .
make[2]: Entering directory `/libevent-2.0.21-stable'
/bin/bash ./libtool --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I.  -I./compat -I./include -I./include    -g -O2 -Wall -fno-strict-aliasing -pthread -MT bufferevent_openssl.lo -MD -MP -MF .deps/bufferevent_openssl.Tpo -c -o bufferevent_openssl.lo bufferevent_openssl.c
libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I./compat -I./include -I./include -g -O2 -Wall -fno-strict-aliasing -pthread -MT bufferevent_openssl.lo -MD -MP -MF .deps/bufferevent_openssl.Tpo -c bufferevent_openssl.c  -fPIC -DPIC -o .libs/bufferevent_openssl.o
bufferevent_openssl.c: In function 'bio_bufferevent_new':
bufferevent_openssl.c:106:3: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:107:3: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:108:3: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:109:3: error: dereferencing pointer to incomplete type
bufferevent_openssl.c: In function 'bio_bufferevent_free':
bufferevent_openssl.c:119:7: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:120:8: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:120:19: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:121:22: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:122:4: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:123:4: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:124:4: error: dereferencing pointer to incomplete type
bufferevent_openssl.c: In function 'bio_bufferevent_read':
bufferevent_openssl.c:140:8: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:143:33: error: dereferencing pointer to incomplete type
bufferevent_openssl.c: In function 'bio_bufferevent_write':
bufferevent_openssl.c:159:31: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:165:8: error: dereferencing pointer to incomplete type
bufferevent_openssl.c: In function 'bio_bufferevent_ctrl':
bufferevent_openssl.c:191:31: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:196:10: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:199:4: error: dereferencing pointer to incomplete type
bufferevent_openssl.c: At top level:
bufferevent_openssl.c:228:1: error: variable 'methods_bufferevent' has initializer but incomplete type
bufferevent_openssl.c:229:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:229:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:229:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:229:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:230:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:230:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:231:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:231:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:232:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:232:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:233:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:233:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:234:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:234:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:235:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:235:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:236:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:236:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c:237:2: warning: excess elements in struct initializer [enabled by default]
bufferevent_openssl.c:237:2: warning: (near initialization for 'methods_bufferevent') [enabled by default]
bufferevent_openssl.c: In function 'BIO_new_bufferevent':
bufferevent_openssl.c:257:8: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:258:8: error: dereferencing pointer to incomplete type
bufferevent_openssl.c:259:8: error: dereferencing pointer to incomplete type

查看106行文件，是BIO *h

static int
bio_bufferevent_new(BIO *b)
{
    b->init = 0;
    b->num = -1;
    b->ptr = NULL; /* We'll be putting the bufferevent in this field.*/
    b->flags = 0;
    return 1;
}

但是我的/usr/include/openssl目录下执行ls，发现是存在bio.h

执行openssl version -a：

OpenSSL 1.1.0g  2 Nov 2017
built on: reproducible build, date unspecified
platform: dist
compiler: cc -DNDEBUG -DOPENSSL_NO_DYNAMIC_ENGINE -DOPENSSLDIR="\"/usr/local/ssl\"" -DENGINESDIR="\"/usr/local/lib/engines-1.1\"" 
OPENSSLDIR: "/usr/local/ssl"
ENGINESDIR: "/usr/local/lib/engines-1.1"

目前就不知道怎么回事了
编译环境是linux，各位给个提示，怎么查问题？

Answer 1

这是 libevent 与 openssl 版本不兼容导致。

一般来说，它们的版本关系是这样的

libevent	openssl
2.1.x	1.1
2.0.x	1.0

因此你有两个选择

1. 使用 libevent 2.1.x 版本，这与你本机的 openssl 1.1 匹配，无需任何修改直接编译即可。
2. 使用 libevent 2.0.x 版本，你需要安装 openssl 1.0 版本，然后在编译时指定链接版本。

---

下面针对第二种选择做详细说明，这种方法是通用的，适用于编译其他软件时出现版本不兼容问题。

1. 首先安装 openssl 1.0 版本，注意需要头文件。你可以选择从源码安装，或使用操作系统的仓库下载安装。
   这类安装包通常带有 "*-dev" 字样，比如 centos 发行版可能是这样的

   yum install openssl-devel-1.0xxx

2. openssl 安装完成后，会有一个 pkgconfig/ 目录，实际路径取决于你上一步的操作，一般位于 /usr/lib 或 /usr/local/lib 下。
   这里我们假设是 /usr/local/lib/openssl-1.0/pkgconfig/， 你需要将它设置成 PKG_CONFIG_PATH 的环境变量值，如

   export PKG_CONFIG_PATH=/usr/local/lib/openssl-1.0/pkgconfig/ 

3. 切换到 libevent 源码目录，把 openssl 头文件路径，及库文件路径加入 configure 配置变量，如

   ./configure   CFLAGS="$(pkg-config --cflags openssl)"   LDFLAGS="$(pkg-config --libs openssl)"

4. 清除原内容，并重新编译即可

   make clean
   make -j8