memcached——与c++对接，建立连接

参考官方文档：http://docs.libmemcached.org/index.html

根据菜鸟教程上介绍，c++实现了连接memcached的客户端。

通过apt-cache search，查到到了需要安装的库

root@iZwz9aujzgp9b5o38x29akZ:~# apt-cache search memcached | grep C++
libmemcached-dev - C and C++ client library to the memcached server (development files)
libmemcached11 - C and C++ client library to the memcached server

于是分别安装了libmemcached-dev与libmemcached11

root@iZwz9aujzgp9b5o38x29akZ:~# apt-get install libmemcached11
.....//略
root@iZwz9aujzgp9b5o38x29akZ:~# apt-get install libmemcached-dev
.....//略

然后找到头文件

root@iZwz9aujzgp9b5o38x29akZ:~# cd /usr/include/libmemcached/
root@iZwz9aujzgp9b5o38x29akZ:/usr/include/libmemcached# ll
total 20
drwxr-xr-x  2 root root 4096 Jan 19 19:16 ./
drwxr-xr-x 40 root root 4096 Jan 19 19:15 ../
-rw-r--r--  1 root root 1713 Jan 18  2019 memcached.h
-rw-r--r--  1 root root 1717 Jan 18  2019 memcached.hpp
-rw-r--r--  1 root root 1714 Jan 18  2019 util.h

与libmemcached官方文档相符

接下来就是要写个测试程序，连上memcached

根据官方文档的资源，写了如下测试程序

vim connect_to_memcached.cpp 

#include <iostream>
  
#include <string.h>
#include <libmemcached/memcached.h>

using namespace std;
int main()
{
        const char * config_string = "--SERVER=127.0.0.1";
        memcached_st * memc = NULL;
        cout << static_cast<const void *>(memc) << endl;
        memc = memcached(config_string, strlen(config_string));
        cout << static_cast<const void *>(memc) << endl;
        memcached_free(memc);
        cout << static_cast<const void *>(memc) << endl;
        return 0;
}

编译

g++ connect_to_memcached.cpp -o connect_to_memcached.exe            
/tmp/ccf2s5UM.o: In function `main':
connect_to_memcached.cpp:(.text+0x2d): undefined reference to `memcached'
connect_to_memcached.cpp:(.text+0x3d): undefined reference to `memcached_free'
collect2: error: ld returned 1 exit status

这里报错了，是因为没有链接其动态库，最终链接失败

g++ connect_to_memcached.cpp -lmemcached -o connect_to_memcached.exe

编译成功。执行./connect_to_memcached.exe 

root@iZwz9aujzgp9b5o38x29akZ:~/memcached_cpp# ./connect_to_memcached.exe 
0
0x557ca3ff3280
0x557ca3ff3280

说明memcached()给其分配了空间。为了证明连接上了，需要再从memcache里取点数据看看

#include <iostream>

#include <string.h>
#include <libmemcached/memcached.h>

using namespace std;

int main()
{
        const char * config_string = "--SERVER=127.0.0.1";
        memcached_st * memc = memcached(config_string, strlen(config_string)); 
        memcached_return_t ret;
        const char * key = "name";
        size_t value_len;
        uint32_t flags;
        char * value = memcached_get(memc, key, strlen(key), &value_len, &flags, &ret);
        cout << "key:" << key << endl;
        cout << "ret:" << ret << endl;

        if(memcached_success(ret))
        {
                cout << "value:" << value << endl;
                cout << "value_len:" << value_len << endl;
                cout << "flags:" << flags << endl;
        }
        else
        {
                cout << "memcached_get fail" << endl;
        }

        memcached_free(memc);
        return 0;
}

root@iZwz9aujzgp9b5o38x29akZ:~/memcached_cpp# g++ connect_to_memcached.cpp -lmemcached -o connect_to_memcached.exe
root@iZwz9aujzgp9b5o38x29akZ:~/memcached_cpp# ./connect_to_memcached.exe 
key:name
ret:0
value:ccx
value_len:3
flags:0