注意!PHP中字符串與數字的比較

在平常開發過程當中,運算符是咱們天天都會接觸到的。這個運算符中其實埋了很是多的坑,今天咱們就來看下字符串和數字用比較須要注意的問題。php

首先來看看這些代碼:git

echo '"1234" == " 1234" is ' . ('1234' == ' 1234'), PHP_EOL;
echo '"1234" == "\n1234" is ' . ('1234' == "\n1234"), PHP_EOL;
echo '"1234" == "1234" is ' . ('1234' == '1234'), PHP_EOL;
echo '"1234" == "1234 " is ' . ('1234' == '1234 '), PHP_EOL;
echo '"1234" == "1234\n" is ' . ('1234' == "1234\n"), PHP_EOL;

都是字符串的==操做,它們的結果會是什麼呢?github

"1234" == " 1234" is 1
"1234" == "\n1234" is 1
"1234" == "1234" is 1
"1234" == "1234 " is 
"1234" == "1234\n" is

沒錯,空格或者製表符號在前的會忽略掉這些符號,也就是說,這些字符串在對比的時候進行了類型轉換,都被強轉成了int型。而特殊字符在後的,則會按照字符串類型進行比對,那麼,純字符類型呢?微信

echo '"aa" == " aa" is ' . ('aa' == ' aa'), PHP_EOL;
echo '"aa" == "\naa" is ' . ('a' == '\naa'), PHP_EOL;
echo '"aa" == "aa" is ' . ('aa' == 'aa'), PHP_EOL;
echo '"aa" == "aa " is ' . ('aa' == 'aa '), PHP_EOL;
echo '"aa" == "aa\n" is ' . ('aa' == "aa\n"), PHP_EOL;

這時候的結果就符合咱們的預期了,他們自己就是字符串的比對,不會進行任何類型的轉換:學習

"aa" == " aa" is 
"aa" == "\naa" is 
"aa" == "aa" is 1
"aa" == "aa " is 
"aa" == "aa\n" is

綜上實驗結果得知,當字符串的內容都是int數據時,字符串的==比較會忽略在字符串前面出現的空格或者製表符號將它們強制轉換成int類型。而只要字符串中包含文本或者特殊符號在數字的後面,就會以文本方式進行比較,如純文本或者混合文本("11aa"、"11\n"、"aa11 ")。測試

測試代碼:https://github.com/zhangyue0503/dev-blog/blob/master/php/201910/source/%E6%B3%A8%E6%84%8F%EF%BC%81PHP%E4%B8%AD%E5%AD%97%E7%AC%A6%E4%B8%B2%E4%B8%8E%E6%95%B0%E5%AD%97%E7%9A%84%E6%AF%94%E8%BE%83.php.net

參考連接:https://www.php.net/manual/zh/language.operators.comparison.php

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