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背景：如果要用c写成一个服务部署4台机器，均得和memcached交互，还得用这个库，如PHP的扩展啥的没怎么和c的lib打交到，这下实践一下挺好的，过程比较曲折但是也发现了这memcached用新的gcc还是对配置上有一些影响的，就单说配置这块的门槛就变高了，更别说c下的调试啥的，实践起来仅仅通过网上的一篇文章未必能搞定。
libmemcached是C客户端到memcached服 务器的接口库。具有低内存占用率、线程安全、并提供对memcached功能的全面支持。它还采用多种命令行工具，包括： memcat、memflush、memrm、memstat、memslap。
在Ubuntu上安装memcached和libmemcached  http://www.linuxidc.com/Linux/2010-04/25543.htm
libmemcached C/C++ API使用实例 http://www.linuxidc.com/Linux/2012-01/52516.htm
memcached简单的使用教程(转载):          http://blog.csdn.net/huangqiwa/article/details/21174425
使用连接池访问memcached(libmemcached)的完整例子:http://blog.csdn.net/hzhxxx/article/details/41961355

（1）封装 libmemcached 构建 memcached 客户端：http://blog.csdn.net/yanghw0510/article/details/7292236
（2）libmemcached使用（c 客户端连接 memcached） :
（3）libmemcached 下载地址。https://launchpad.net/libmemcached/

1、下载安装libmemcached
$ wget http://launchpad.net/libmemcached/1.0/0.44/+download/libmemcached-0.44.tar.gz
$ tar xvzf libmemcached-0.44tar.gz
$ cd libmemcached-0.44
$ ./configure
$ make
$ sudo make install
libmemcached 默认安装在/usr/local/,头文件安装在/usr/local/include/libmemcachde/,动态库默认安装在/usr/local/lib/下。
我在这儿下的：https://launchpadlibrarian.net/165454254/libmemcached-1.0.18.tar.gz
注:
如果报”./libmemcached-1.0/memcached.h:46:27: error: tr1/cinttypes: No such file or directory”错误,则需要升级gcc版本.
处理如下：
yum install gcc44 gcc44-c++ libstdc++44-devel
export CC=/usr/bin/gcc44
export CXX=/usr/bin/g++44
重新编译安装libmemcached-1.0.9
关键信息：error: tr1/cinttypes: No such file or directory
报错原因：libmemcached需要 gcc 4.2 以上版本才可编译，而centos 5.4 的gcc版本只有4.1 ，详见：https://bugs.launchpad.net/libmemcached/+bug/1076181
解决方法：安装gcc44的扩展包，详见：http://gearman.info/build/centos5-8.html
export就是在于此，把这个gcc和g++的版本号给提上去，以方便这个memcached的编译：
/usr/bin/gcc44 -v
gcc version 4.4.7 20120313 (Red Hat 4.4.7-1) (GCC)

gcc -v
gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)

/usr/bin/g++44 -v
gcc version 4.4.7 20120313 (Red Hat 4.4.7-1) (GCC)
g++ -v
gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)
——————————————————————————————————————————————————————————
这个问题在安gearman时也遇到过，升级gcc，参考连接： http://jackxiang.com/post/7693/ ，软链接如下所示：
export CC=/usr/bin/gcc44 or export CC=/usr/bin/gcc
export CXX=/usr/bin/g++44
./configure && make && make install      

./configure && make && make install
/usr/bin/install -c -m 644 support/libmemcached.pc '/usr/local/lib/pkgconfig'
make[2]: Leaving directory `/tmp/testmemcachedcpp/libmemcached-1.0.18'
make[1]: Leaving directory `/tmp/testmemcachedcpp/libmemcached-1.0.18'

g++ -o testmemcached testmemcached.cpp -lmemcached  
In file included from /usr/local/include/libmemcached/memcached.h:39,
                 from testmemcached.cpp:6:
/usr/local/include/libmemcached-1.0/memcached.h:46:23: error: cinttypes: No such file or directory
明天再整下，估计是so没有给ldd进来...
2、libmemcached简单测试使用
//g++ -o testmemcached testmemcached.cpp -lmemcached ///usr/bin/g++44 -g  -o testmemcached testmemcached.cpp -lmemcached -lrt  -std=c++0x #include <iostream> #include <string> #include <libmemcached/memcached.h> using namespace std; int main(int argc,char *argv[]) {    //connect server    memcached_st *memc;    memcached_return rc;    memcached_server_st *server;    time_t expiration;    uint32_t flags;    memc = memcached_create(NULL);    server = memcached_server_list_append(NULL,"localhost",11211,&rc);    rc=memcached_server_push(memc,server);    memcached_server_list_free(server);    string key = "key";    string value = "value";    size_t value_length = value.length();    size_t key_length = key.length();    //Save data    rc=memcached_set(memc,key.c_str(),key.length(),value.c_str(),value.length(),expiration,flags);    if(rc==MEMCACHED_SUCCESS)    {        cout<<"Save data:"<<value<<" sucessful!"<<endl;    }    //Get data    char* result = memcached_get(memc,key.c_str(),key_length,&value_length,&flags,&rc);    if(rc == MEMCACHED_SUCCESS)    {        cout<<"Get value:"<<result<<" sucessful!"<<endl;    }    //Delete data    rc=memcached_delete(memc,key.c_str(),key_length,expiration);    if(rc==MEMCACHED_SUCCESS)    {        cout<<"Delete key:"<<key<<" sucessful!"<<endl;    }    //free    memcached_free(memc);    return 0; }

编译：g++ -o testmemcached testmemcached.cpp -lmemcached
运行：./testmemcached
结果：Save data:value sucessful!
      Get value:value sucessful!
      Delete key:key sucessful!

实践编译一下：
g++ -o testmemcached testmemcached.cpp -lmemcached
In file included from /usr/local/include/libmemcached/memcached.h:39,
                 from testmemcached.cpp:6:
/usr/local/include/libmemcached-1.0/memcached.h:46:23: error: cinttypes: No such file or directory
看来还得重新export一次新的编译器，因为昨天的关了终端，今天的又没了：
export CC=/usr/bin/gcc44 or export CC=/usr/bin/gcc  //这行有问题~
export CXX=/usr/bin/g++44
g++ -o testmemcached testmemcached.cpp -lmemcached
为何还是不行？
echo $CC
/usr/bin/gcc  //没变，这儿有问题，再重新设置一次，查到上面这个or有问题：export CC=/usr/bin/gcc44。
# echo $CXX
/usr/bin/g++44 //变了

重新设置，好了：
export CC=/usr/bin/gcc44
/usr/bin/gcc44

继续折腾，/usr/bin/gcc44 -o testmemcached testmemcached.cpp -lmemcached
In file included from /usr/lib/gcc/x86_64-redhat-linux6E/4.4.7/../../../../include/c++/4.4.7/cinttypes:35,
                 from /usr/local/include/libmemcached-1.0/memcached.h:46,
                 from /usr/local/include/libmemcached/memcached.h:39,
                 from testmemcached.cpp:6:
/usr/lib/gcc/x86_64-redhat-linux6E/4.4.7/../../../../include/c++/4.4.7/c++0x_warning.h:31:2: error: #error This file requires compiler and library support for the upcoming ISO C++ standard, C++0x. This support is currently experimental, and must be enabled with the -std=c++0x or -std=gnu++0x compiler options.


#error This file requires compiler and library support for the upcoming ISO C++ standard, C++0x.
加上：-lpthread -std=c++0x ，解决如下：
g++ -o testmemcached testmemcached.cpp -lmemcached -lpthread -std=c++0x
/usr/bin/ld: cannot find -lmemcached
collect2: ld returned 1 exit status  
也就是说编译器并不能从ldconfig 里得知，其lib在哪儿（及时把Lib路径加入到/etc/ld.so.conf.d/libmemcache.conf），得指定：
g++ -o testmemcached testmemcached.cpp -lmemcached -lpthread -std=c++0x  -L/usr/local/libmemcached/lib/ ldconfig -p|grep memcache libmemcached.so (libc6,x86-64) => /usr/local/libmemcached/lib/libmemcached.so   AddTime:2017-08-01

在网上找了一下，发现是这样的：http://blog.163.com/guixl_001/blog/static/4176410420121021111117987/ 里说得加一个新的参数，是和宏相关，那就加了，
指定一个新的参数：-std=c++0x :
/usr/bin/gcc44  -o testmemcached testmemcached.cpp -lmemcached   -std=c++0x            
/usr/local/lib/libmemcached.so: undefined reference to `pthread_once'
collect2: ld returned 1 exit status


/usr/bin/g++44  -o testmemcached testmemcached.cpp -lmemcached   -std=c++0x              
/usr/local/lib/libmemcached.so: undefined reference to `pthread_once'
怎样彻底解决"undefined reference to `pthread_create'"问题 ，说是加个： -lrt ，这一看就是那个memcached的库包含了这个文件：#include<pthread.h>
来源参考：
http://bbs.chinaunix.net/thread-1586752-1-1.html

于是Ok啦，最终O了，如下：
[root@test testmemcachedcpp]# /usr/bin/g++44  -o testmemcached testmemcached.cpp -lmemcached -lrt  -std=c++0x
[root@test testmemcachedcpp]#  
运行一下试试：
[root@test testmemcachedcpp]#  ./testmemcached
./testmemcached: error while loading shared libraries: libmemcached.so.11: cannot open shared object file: No such file or directory
[root@test /]# find . -name "libmemcached.so.11"
./usr/local/lib/libmemcached.so.11
打开配置文件 vi /etc/ld.so.conf
加上一行：/usr/local/lib
执行/sbin/ldconfig /etc/ld.so.conf
[root@test testmemcachedcpp]# /sbin/ldconfig /etc/ld.so.conf
[root@test testmemcachedcpp]# ./testmemcached              
[root@test testmemcachedcpp]#
没报错了~，用gdb看一下 加个-g参数：
/usr/bin/g++44 -g  -o testmemcached testmemcached.cpp -lmemcached -lrt  -std=c++0x

发现localhost没有开11211，于是找了一台机器把ip和端口写上，重新编译一次后运行Ok，如下：
[root@test testmemcachedcpp]# ./testmemcached
Save data:value sucessful!
Get value:value sucessful!

少了一个删除成功的，简单调试一下：
(gdb) n
Get value:value sucessful!
50         rc=memcached_delete(memc,key.c_str(),key_length,expiration);
(gdb) p key.c_str()
$5 = 0x184372e8 "key"
(gdb) p key_length
$6 = 3
(gdb) n
51         if(rc==MEMCACHED_SUCCESS)
(gdb) p rc
$3 = MEMCACHED_INVALID_ARGUMENTS

也就是调这个函数的参数不对，返回不是MEMCACHED_SUCCESS，所以没有打印出：cout<<"Delete key:"<<key<<" sucessful!"<<endl;

####################新的代码里grep了一下该方法###########################
./tests/mem_udp.cc:                 memcached_delete(memc, test_literal_param("foo"), 0));
./libmemcached-1.0/memcached.hpp:    return memcached_success(memcached_delete(memc_, key.c_str(), key.length(), 0));
./libmemcached-1.0/memcached.hpp:    return memcached_success(memcached_delete(memc_,
./tests/libmemcached-1.0/replication.cc:    memcached_return_t del_rc= memcached_delete(memc_replicated,
./tests/libmemcached-1.0/mem_functions.cc:    rc= memcached_delete(memc, "foo", 3, 1);

./tests/libmemcached-1.0/mem_functions.cc:    test_compare(MEMCACHED_BUFFERED, (rc= memcached_delete(memc, "foo", 3, 0)));
./tests/libmemcached-1.0/mem_functions.cc:    test_compare(MEMCACHED_SUCCESS, memcached_delete(memc, "foo", 3, 0));
./tests/libmemcached-1.0/mem_functions.cc:    test_compare(MEMCACHED_NOTFOUND, memcached_delete(memc, "foo", 3, 0));

####################################################################
于是修改为下面这样：
//rc=memcached_delete(memc,key.c_str(),key_length,expiration);
rc=memcached_delete(memc,key.c_str(),key_length,0);

./testmemcached
Save data:value2 sucessful!
Get value:value2 sucessful!
Delete key:key sucessful!

刚才失败时有值，现在运行后没值了，给成功删除了：
[root@localhost ~]# telnet 192.168.108.7 11211
Escape character is '^]'.
get key
VALUE key 0 5
value
END
get key
END



后面怎么结合c的socket 及epoll进行进程/线程调试就不再细说了，我也在摸索中，应该也有相关的调试办法，但这儿说明这个memcached搞个新的gcc版本库才能编译确实带了相当多编译及配置上的的麻烦~

最后，用C函数里的add函数实现类php的memcache的扩展的原子操作函数，如下：
原子操作方法，假如有add后就不能再add，必须删除后才能add，这个可以用作锁：
./libmemcached-1.0.18/libmemcached-1.0/memcached.hpp:    
return memcached_success(memcached_add(memc_, key.c_str(), key.length(),   /**    * Add an object with the specified key and value to the server. This    * function returns false if the object already exists on the server.    *    * @param[in] key key of object to add    * @param[in] value of object to add    * @return true on success; false otherwise    */   bool add(const std::string& key, const std::vector<char>& value)   {     return memcached_success(memcached_add(memc_, key.c_str(), key.length(),                                                                                                                                                                    &value[0], value.size(), 0, 0));   }

和php的add函数一样第一次运行时没有问题此时值设置成功，再运行add时一次就add不进去，add设置进去后，用set是能重新设置进去的，只是用add原子操作是不行的，用它来做锁很好使：
1）代码片段：
//add data,then test set data error rc=memcached_add(memc,key.c_str(),key.length(),value.c_str(),value.length(),expiration,flags); if(rc==MEMCACHED_SUCCESS) {      cout<<"Add data:"<<value<<" sucessful!"<<endl; }else{       cout<<"Add data:"<<value<<" unsucessful,Perhaps add key before set !"<<endl; }
2）运行情况：
[root@test testmemcachedcpp]# gdb testmemcached
b 41
r
Add data:value unsucessful,Perhaps add key before set !
(gdb) p rc
$2 = MEMCACHED_NOTSTORED
但是能够set进去：
42         rc=memcached_set(memc,key.c_str(),key.length(),value.c_str(),value.length(),expiration,flags);
(gdb) n
43         if(rc==MEMCACHED_SUCCESS)
(gdb) p rc
$3 = MEMCACHED_SUCCESS
EOF


对add后的键对应的值，再用set方法是可以设置的，如下：
string key = "key2";
string value = "jackxiang";
rc=memcached_add(memc,key.c_str(),key.length(),value.c_str(),value.length(),expiration,flags);
后再修改这个值：
value = "xiangdong";
rc=memcached_set(memc,key.c_str(),key.length(),value.c_str(),value.length(),expiration,flags);

用gdb的断点跟踪一下并用telnet在设置后查看，如下：
[root@localhost ~]# telnet 192.168.108.7 11211
Escape character is '^]'.
get key2
END
get key2
VALUE key2 0 9
jackxiang
END
get key2
VALUE key2 0 9
xiangdong
END

听说，在下载客户端libmemcached-1.0.18/tests 下有测试列子，也可参考。比如cpp_example.cc
ls ~+/cpp_example.cc
/tmp/testmemcachedcpp/libmemcached-1.0.18/tests/cpp_example.cc

摘自：http://www.cppblog.com/kefeng/archive/2010/10/11/129422.html
         http://blog.chinaunix.net/uid-52437-id-2108905.html
后发现这个哥们写的文章很详细，http://blog.chinaunix.net/uid-20548989-id-1667248.html

加入add后，rc=MEMCACHED_NOTSTORED情况，代码贴下面：
//g++ -o testmemcached testmemcached.cpp -lmemcached ///usr/bin/g++44 -g  -o testmemcached testmemcached.cpp -lmemcached -lrt  -std=c++0x #include <iostream> #include <string> #include <libmemcached/memcached.h> using namespace std; int main(int argc,char *argv[]) {     //connect server     memcached_st *memc;     memcached_return rc;     memcached_server_st *server;     time_t expiration;     uint32_t flags;     memc = memcached_create(NULL);     //server = memcached_server_list_append(NULL,"192.168.109.7",11211,&rc);     server = memcached_server_list_append(NULL,"192.168.109.7",21211,&rc);//TTServer     rc=memcached_server_push(memc,server);     memcached_server_list_free(server);     string key = "key";     string value = "value";     size_t value_length = value.length();     size_t key_length = key.length();     //add data,then test set data error     rc=memcached_add(memc,key.c_str(),key.length(),value.c_str(),value.length(),expiration,flags);     if(rc==MEMCACHED_SUCCESS)     {         cout<<"Add data:"<<value<<" sucessful!"<<endl;     }else{         cout<<"Add data:"<<value<<" unsucessful,Perhaps add key before set !"<<endl;     }     //Save data     rc=memcached_set(memc,key.c_str(),key.length(),value.c_str(),value.length(),expiration,flags);     if(rc==MEMCACHED_SUCCESS)     {         cout<<"Save data:"<<value<<" sucessful!"<<endl;     }     //Get data     char* result = memcached_get(memc,key.c_str(),key_length,&value_length,&flags,&rc);     if(rc == MEMCACHED_SUCCESS)     {         cout<<"Get value:"<<result<<" sucessful!"<<endl;     }     //Delete data     //rc=memcached_delete(memc,key.c_str(),key_length,expiration);     rc=memcached_delete(memc,key.c_str(),key_length,0);     if(rc==MEMCACHED_SUCCESS)     {         cout<<"Delete key:"<<key<<" sucessful!"<<endl;     }     //free     memcached_free(memc);     return 0; }

作者：jackxiang@向东博客 专注WEB应用 构架之美 --- 构架之美，在于尽态极妍 | 应用之美，在于药到病除
地址：https://jackxiang.com/post/7814/
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