摘要：
在前一篇文章中，讲述了如何进行mysql源程序代码的编译链接，但是没有讲述运行情况，在按照上一篇文章代码下进行编译运行后，发现无法链接数据库文件，显然是在mysql_real_connect（）函数中出现了问题。在mysql的英文手册中找到关于mysql_real_connect()的如下描述：在前一篇文章中，讲述了如何进行mysql源程序代码的编译链接，但是没有讲述运行情况，在按照上一篇文章代码下进行编译运行后，发现无法链接数据库文件，显然是在mysql_real_connect（）函数中出现了问题。
//函数原型描述
MYSQL*mysql_real_connect(MYSQL*mysql,constchar*host,constchar*user, constchar*passwd,constchar*db,unsignedintport,constchar*unix_socket,
unsignedlongclient_flag)
Descriptionmysql_real_connect()attemptstoestablishaconnectiontoaMySQLdatabaseengine runningonhost.mysql_real_connect()mustcompletesuccessfullybeforeyoucan
executeanyotherAPIfunctionsthatrequireavalidMYSQLconnectionhandlestructure.
Theparametersarespecifiedasfollows:*ThefirstparametershouldbetheaddressofanexistingMYSQLstructure.Beforecallingmysql_real_connect()youmustcallmysql_init()toinitializetheMYSQL
structure.Youcanchangealotofconnectoptionswiththemysql_options()call.
SeeSectionÂ17.2.3.47,“mysql_options()”.
*ThevalueofhostmaybeeitherahostnameoranIPaddress.IfhostisNULLorthe string"localhost",aconnectiontothelocalhostisassumed.IftheOSsupportssockets
(Unix)ornamedpipes(Windows),theyareusedinsteadofTCP/IPtoconnecttotheserver.
*Theuserparametercontainstheuser'sMySQLloginID.IfuserisNULLortheempty string"",thecurrentuserisassumed.UnderUnix,thisisthecurrentloginname.Under
WindowsODBC,thecurrentusernamemustbespecifiedexplicitly.SeeSectionÂ18.1.9.2,
“ConfiguringaMyODBCDSNonWindows”.
*Thepasswdparametercontainsthepasswordforuser.IfpasswdisNULL,onlyentriesintheusertablefortheuserthathaveablank(empty)passwordfieldarecheckedfora
match.ThisallowsthedatabaseadministratortosetuptheMySQLprivilegesystemin
suchawaythatusersgetdifferentprivilegesdependingonwhethertheyhavespecified
apassword.
Note:Donotattempttoencryptthepasswordbeforecallingmysql_real_connect();passwordencryptionishandledautomaticallybytheclientAPI.
*dbisthedatabasename.IfdbisnotNULL,theconnectionsetsthedefaultdatabase tothisvalue.
*Ifportisnot0,thevalueisusedastheportnumberfortheTCP/IPconnection.Note thatthehostparameterdeterminesthetypeoftheconnection.
*Ifunix_socketisnotNULL,thestringspecifiesthesocketornamedpipethatshouldbeused.Notethatthehostparameterdeterminesthetypeoftheconnection.
*Thevalueofclient_flagisusually0,butcanbesettoacombinationofthefollowing flagstoenablecertainfeatures:
//上面描述了五个参数的主要取值，MYSQL *为mysql_init函数返回的指针，host为null或 // localhost时链接的是本地的计算机，当mysql默认安装在unix（或类unix）系统中，root账户是没// 有密码的，因此用户名使用root，密码为null，当db为空的时候，函数链接到默认数据库，在进行 // mysql安装时会存在默认的test数据库，因此此处可以使用test数据库名称，port端口为0，使用 // unix连接方式，unix_socket为null时，表明不使用socket或管道机制，最后一个参数经常设置为0
changedrows.
CLIENT_IGNORE_SPACEAllowspacesafterfunctionnames.Makesallfunctionsnames reservedwords.
CLIENT_INTERACTIVEAllowinteractive_timeoutseconds(insteadofwait_timeout seconds)ofinactivitybeforeclosingtheconnection.Theclient'ssessionwait_timeout
variableissettothevalueofthesessioninteractive_timeoutvariable.
CLIENT_LOCAL_FILESEnableLOADDATALOCALhandling.CLIENT_MULTI_STATEMENTSTelltheserverthattheclientmaysendmultiple statementsinasinglestring(separatedby‘;’).Ifthisflagisnotset,
multiple-statementexecutionisdisabled.AddedinMySQL4.1.
CLIENT_MULTI_RESULTSTelltheserverthattheclientcanhandlemultipleresult setsfrommultiple-statementexecutionsorstoredprocedures.Thisisautomatically
setifCLIENT_MULTI_STATEMENTSisset.AddedinMySQL4.1.
CLIENT_NO_SCHEMADon'tallowthedb_name.tbl_name.col_namesyntax.Thisisfor ODBC.Itcausestheparsertogenerateanerrorifyouusethatsyntax,whichisuseful
fortrappingbugsinsomeODBCprograms.
CLIENT_ODBCTheclientisanODBCclient.ThischangesmysqldtobemoreODBC-friendly.
CLIENT_SSLUseSSL(encryptedprotocol).Thisoptionshouldnotbesetby applicationprograms;itissetinternallyintheclientlibrary.Instead,use
mysql_ssl_set()beforecallingmysql_real_connect().
Forsomeparameters,itispossibletohavethevaluetakenfromanoptionfilerather thanfromanexplicitvalueinthemysql_real_connect()call.Todothis,call
mysql_options()withtheMYSQL_READ_DEFAULT_FILEorMYSQL_READ_DEFAULT_GROUPoption
beforecallingmysql_real_connect().Then,inthemysql_real_connect()call,specify
the“no-value”valueforeachparametertobereadfromanoptionfile:
*Forhost,specifyavalueofNULLortheemptystring("").*Foruser,specifyavalueofNULLortheemptystring.*Forpasswd,specifyavalueofNULL.(Forthepassword,avalueoftheemptystringinthemysql_real_connect()callcannotbeoverriddeninanoptionfile,becausetheempty
stringindicatesexplicitlythattheMySQLaccountmusthaveanemptypassword.)
*Fordb,specifyavalueofNULLortheemptystring.*Forport,specifyavalueof0.*Forunix_socket,specifyavalueofNULL.Ifnovalueisfoundinanoptionfileforaparameter,itsdefaultvalueisusedasindicatedinthedescriptionsgivenearlierinthissection.
ReturnValuesAMYSQL*connectionhandleiftheconnectionwassuccessful,NULLiftheconnection wasunsuccessful.Forasuccessfulconnection,thereturnvalueisthesameasthevalue
ofthefirstparameter.
// 返回值：当连接成功时，返回MYSQL连接句柄，失败，返回NULL。当成功时，返回值与第一个参数值是// 相同的。
Errors*CR_CONN_HOST_ERRORFailedtoconnecttotheMySQLserver.*CR_CONNECTION_ERRORFailedtoconnecttothelocalMySQLserver.*CR_IPSOCK_ERRORFailedtocreateanIPsocket.*CR_OUT_OF_MEMORYOutofmemory.*CR_SOCKET_CREATE_ERRORFailedtocreateaUnixsocket.*CR_UNKNOWN_HOSTFailedtofindtheIPaddressforthehostname.*CR_VERSION_ERRORAprotocolmismatchresultedfromattemptingtoconnecttoaserverwithaclient librarythatusesadifferentprotocolversion.Thiscanhappenifyouuseaveryold
clientlibrarytoconnecttoanewserverthatwasn'tstartedwiththe--old-protocol
option.
*CR_NAMEDPIPEOPEN_ERRORFailedtocreateanamedpipeonWindows.*CR_NAMEDPIPEWAIT_ERRORFailedtowaitforanamedpipeonWindows.*CR_NAMEDPIPESETSTATE_ERRORFailedtogetapipehandleronWindows.*CR_SERVER_LOSTIfconnect_timeout>0andittooklongerthanconnect_timeoutsecondstoconnectto theserveroriftheserverdiedwhileexecutingtheinit-command.
mysql_real_connect(mysql,"localhost","root",NULL,"test",0,NULL,0);
判断是否出错，出错调用mysql_error()
函数显示出错信息，或使用mysql_errno()函数获取出错代号。