出于某种原因，我的条件语句在计算 false 时不是
$file_check=strpos(file_get_contents("database/file_register.txt"),basename($_FILES["fileToUpload"]["name"]));
echo "file=$file_check"; '' equals 0 -> which is not False.
if(isset($_POST["submit"]) && ($file_check == False)) {$file_check='ok';}
else{echo "The document is already in use.";}
echo "file=$file_check"; '' now it equals 'ok'
您的条件是检查0 == False是否为真
确保设置submit
PHP 类型比较表
$x与PHP函数的比较
+------------------+------------+----------+------------+----------+------------------+
| Expression | gettype() | empty() | is_null() | isset() | boolean : if($x) |
+------------------+------------+----------+------------+----------+------------------+
| $x = ""; | string | TRUE | FALSE | TRUE | FALSE |
| $x = null; | NULL | TRUE | TRUE | FALSE | FALSE |
| var $x; | NULL | TRUE | TRUE | FALSE | FALSE |
| $x is undefined | NULL | TRUE | TRUE | FALSE | FALSE |
| $x = array(); | array | TRUE | FALSE | TRUE | FALSE |
| $x = false; | boolean | TRUE | FALSE | TRUE | FALSE |
| $x = true; | boolean | FALSE | FALSE | TRUE | TRUE |
| $x = 1; | integer | FALSE | FALSE | TRUE | TRUE |
| $x = 42; | integer | FALSE | FALSE | TRUE | TRUE |
| $x = 0; | integer | TRUE | FALSE | TRUE | FALSE |
| $x = -1; | integer | FALSE | FALSE | TRUE | TRUE |
| $x = "1"; | string | FALSE | FALSE | TRUE | TRUE |
| $x = "0"; | string | TRUE | FALSE | TRUE | FALSE |
| $x = "-1"; | string | FALSE | FALSE | TRUE | TRUE |
| $x = "php"; | string | FALSE | FALSE | TRUE | TRUE |
| $x = "true"; | string | FALSE | FALSE | TRUE | TRUE |
| $x = "false"; | string | FALSE | FALSE | TRUE | TRUE |
+------------------+------------+----------+------------+----------+------------------+
== VS ===
- 松散比较仅考虑值。
- 严格比较考虑了值和类型
与==的松散比较
+----------+--------+--------+--------+--------+--------+--------+--------+--------+--------+----------+--------+-------+
| | TRUE | FALSE | 1 | 0 | -1 | "1" | "0" | "-1" | NULL | array() | "php" | "" |
+----------+--------+--------+--------+--------+--------+--------+--------+--------+--------+----------+--------+-------+
| TRUE | TRUE | FALSE | TRUE | FALSE | TRUE | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE |
| FALSE | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | TRUE | TRUE | FALSE | TRUE |
| 1 | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE |
| 0 | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | TRUE | FALSE | TRUE | TRUE |
| -1 | TRUE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE |
| "1" | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE |
| "0" | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE |
| "-1" | TRUE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE |
| NULL | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | TRUE | TRUE | FALSE | TRUE |
| array() | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | TRUE | FALSE | FALSE |
| "php" | TRUE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE |
| "" | FALSE | TRUE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | TRUE |
+----------+--------+--------+--------+--------+--------+--------+--------+--------+--------+----------+--------+-------+
与===严格比较
+----------+--------+--------+--------+--------+--------+--------+--------+--------+--------+----------+--------+-------+
| | TRUE | FALSE | 1 | 0 | -1 | "1" | "0" | "-1" | NULL | array() | "php" | "" |
+----------+--------+--------+--------+--------+--------+--------+--------+--------+--------+----------+--------+-------+
| TRUE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE |
| FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE |
| 1 | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE |
| 0 | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE |
| -1 | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE |
| "1" | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE |
| "0" | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE | FALSE |
| "-1" | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE | FALSE |
| NULL | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE | FALSE |
| array() | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE | FALSE |
| "php" | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE | FALSE |
| "" | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | FALSE | TRUE |
+----------+--------+--------+--------+--------+--------+--------+--------+--------+--------+----------+--------+-------+
参考： http://php.net/manual/en/types.comparisons.php
if（isset（$_POST["submit"]） && （$file_check === False）） { $file_check='ok';}
使用 '===' 在 strpos（） 中检查 TRUE 或 FALSE