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Home Backend Development PHP Tutorial 問下php的常識有關問題 echo和$字符串

問下php的常識有關問題 echo和$字符串

Jun 13, 2016 pm 12:14 PM
echo id nbsp select sql

問下php的常識問題 echo和$字符串
問題1:發(fā)現(xiàn)在sql語句中可以帶$號,比如$sql="select?*?from?table?where?id=$id";這個$id是什么時候被解析它的值的呢?
問題2:echo 是php必不可少的調試語句,在什么情況下echo 不能起調式作用呢?比如class中,還有????
------解決思路----------------------
$sql?=?"select?*?from?table?where?id=$id";
右邊串中的?$id?在向左邊的?$sql?賦值時就解析了

echo?的主要作用是輸出運算結果,而不是調試
雖然也可以在調試的時候利用它打印一些中間量來判斷程序運行的情況
php?提供的調試函數(shù)主要有:
var_dump?用于觀察變量的類型和值
debug_zval_dump?用于觀察變量的引用情況
debug_backtrace?生成一個回溯,用于觀察函數(shù)(方法)的調用情況

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