文档介绍：PHP手册中总结性学****笔记：
1、echo()
描述：输出数据到HTML或者到浏览器窗口，其实它不是一个函数，只是一种语言结构，返回值为空void当使用()时只能传递一个参数如echo("he"）,当不使用()是可以输出多个项目，如echo "he","you","I".
2、print()输出数据到HTML或者到浏览器窗口，其实它也不是一个函数，只是一种语言结构，返回值为1，不管你使用()与否，只能输出一个项目。
3、print_r($bianliang[,true])
描述：打印有关一个变量的易于理解的信息，如果设置了第二个参数为true则只是获得输出结果，但是不打印相关内容。当输出变量为整型、字符型、浮点型时，按其原样输出，当输出为数组或者对象时会按一定格式输出键值和元值如输出数组时
Array
(
[0] => 1
[1] => dfd
[2] => Array
(
[0] => dk
[1] => 45
[2] => dfdfdfdf
)
)
如输出对象时
AdodbData Object
(
[mConn] => ADODB_mysql Object
(
[databaseType] => mysql
[dataProvider] => mysql
[hasInsertID] => 1
[hasAffectedRows] => 1
[metaTablesSQL] => SHOW TABLES
[metaColumnsSQL] => SHOW COLUMNS FROM `%s`
[fmtTimeStamp] => 'Y-m-d H:i:s'
[hasLimit] => 1
[hasMoveFirst] => 1
[hasGenID] => 1
[isoDates] => 1
[sysDate] => CURDATE()
[sysTimeStamp] => NOW()
[hasTransactions] =>
[forceNewConnect] =>
[poorAffectedRows] => 1
[clientFlags] => 0
[substr] => substring
[nameQuote] => `
[compat323] =>
[_genIDSQL] => update %s set id=LAST_INSERT_ID(id+1);
[_genSeqSQL] => create table %s (id int not null)
[_genSeqCountSQL] => select count(*) from %s
[_genSeq2SQL] => insert into %s values (%s)
[_dropSeqSQL] => drop table %s
[database] => test
[host] =>
[user] => root
[password] => root
[debug] =>
[maxblobsize] =>
[concat_operator] => +
[length] => length
[random] => rand()
[upperCase] => upper
[fmtDate] => 'Y-m-d'
[true] => 1
[false] => 0