Php - 检查字符串是否为空或第一个字符不等于

Question

如果字符串为空或第一个字符不等于某事，我该如何检查php。 如果我对空字符串$key = ''执行此操作：

if ($key != '' || $key[0] != '_') 

我明白了：

  

未初始化的字符串偏移量：0

Answer 1

isset没有偏移[0]

if ($key != '' || (isset($key[0]) && $key[0] != '_' )) {
   echo "First Character not equal with _";
}

Answer 2

试试这个

if(trim($key)==''||substr( $key, 0, 1)=='_'){
   echo ' string is  empty or start with _';
}else{
    echo 'false';
}

Answer 3

下面的这段代码将检查一个空字符串，还将检查第一个字符。

if ( strlen($str) > 0 ) {

    if ( $str[0] !== $a_char ){
        echo "My first char did not match that char.";
    } else {
        echo "My first char matched that char.";
    }

} else {

    echo 'String is empty. Therefore, no point checking the first character.';

}

Answer 4

<?php
    //$key = "";
    $something = "h";

    if (!isset($key) || substr( $key, 0, 1) !== $something || empty($key) ) {
        echo('undefined / empty string or string starts with: '.$something);;
    } else {
        echo('b');
    }

$something是您要与

进行比较的角色

示例：如果$ key未定义或""