Describes the relationship between php hollow strings and 0, and describes the relationship between php hollow strings.

Describes the relationship between php hollow strings and 0, and describes the relationship between php hollow strings.

Preface

Recently, when dealing with latitude and longitude issues, when creating a table, select the string varchar to store the longitude and latitude. This will pave the way for future problems. Let's take a look at the detailed introduction.

$_x=$row["x"];$_y=$row["y"];if(isset($_x) && isset($_y)){ if($row["y"] == 0 || $row["x"] == 0){  $d=$this->getDistance($row["y"],$row["x"],$y,$x); }elseif(!empty($row["y"]) && !empty($row["x"])){  $d=$this->getDistance($row["y"],$row["x"],$y,$x); }else{  continue; } if($d < $radius){  $list[]= $data[$key]; }}

In fact, I want to filter out the data with null longitude and latitude and retain the data with zero longitude or latitude. However, I found that the data with null longitude and latitude is always included when I print the list data.

After studying for a long time, we found that the latitude and longitude fields are character types. $row['y']== 0 PHP performs automatic conversion when judging, so$row['y']== 0It is correct when null characters are used. Therefore, data with null longitude and latitude is always contained. So how can we remove data with null longitude and latitude?

It is actually very simple as follows:

if(isset($_x) && isset($_y)){ if($row["y"] == "0" || $row["x"] == "0"){  $d=$this->getDistance($row["y"],$row["x"],$y,$x);

Immediately filter out data with null longitude and latitude.

The following describes the code of preg_replace_callback.

$str="sdjfksdf2345";$str=preg_replace_callback ( '/\d{4}/', function ($match){ return $match[0]."ff";}, $str );echo $str;exit;

The code execution result is

sdjfksdf2345ff

This function uses the result of regular expression matching as the parameter of the anonymous function and the returned result as the replacement result.

Summary

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