Question

Undefined variable: sql in D:\phpStudy\php53\1.php on line 16

<?php
$link = mysql_connect("localhost","root","root") or die (mysql_error());
mysql_select_db('ku',$link)or die (mysql_error());
mysql_query("set names utf8");
$file = file('1001.txt');
$d = $c =count($file);
$a = 100;
$sql2 = "INSERT INTO '100' ('id','username','password')VALUES";
foreach($file as $k=>$value){
//$data = preg_split("/\s+/",$value);
$data=explode(',',$value);
$username = trim($data[0]);
$password = trim($data[1]);
//$email = trim($data[2]);
//$key = trim($data[3]);
$sql.=",(null,'$username','$password')";
if($k>$a && $k<$c){
$sql=str_replace("VALUES,","VALUES",$sql2.$sql);
if(mysql_query($sql)){
$dd=$d-=100;
echo $dd."\n";
}
unset($sql);
$a+=100;
}
}
?>

Answer 1

第16行的$sql变量未定义就直接使用了字符串连接。

$sql.=",(null,'$username','$password')";

这句话等于：

$sql = $sql . ",(null,'$username','$password')";

这时候等号后面的$sql就是个未定义变量，所以报了错。

正确做法应该在前面声明这个变量是个字符串：

$sql = '';
$sql.=",(null,'$username','$password')";