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php字符串比较函数

Jun 13, 2016 am 11:18 AM
php use function judgment the difference and string it common method most Compare of

 

比较两个字符串是否相等,最常见的方法就是使用“===”来判断,至于它和“==”的区别,简单来说就是前者强调“identical”类型也要求一样;后者要求“equal”,值相同就可以了,参考【1】。或者使用strcmp来判断,但是这个能够告诉你两个字符串是否相等,但是无法告诉你在那里不同。我的思路是单字符串分割为一个个字母(character),这样比较就能精确知道在那个位置不同了。分隔字符串,使用“str_split”就可以了,语法参考【2】。然后输出结果数组,好处是连空格也会作为数组的元素。我之前的例子就是因为前一个字符串包含2个空格,而后一个只有一个。但是输出的时候看到的显示都是一样的。 也可以按照其他分隔符进行分割,如“explode”或者“preg_split”,

  一般能用 !=, == 比较两个对象是否相等,只所以说是两个对象,是因为他们不一定全部为字符串,也能为整型等等。比如

$a = "joe";
$b = "jerry";
if ($a != $b)
{
    echo "不相等";
}
else
{
    echo "相等";
}

  如果用 !==,===(能看到多了一个等号)比较的话,两个对象的类型要严格相等才能返回true;否则用==,!=则会将字符串自动转换成相应的类型,以便进行比较.

22 == "22"; // 返回 true
22 === "22"; // 返回false

  正因为这样,所以我们的程式时常会发生一些想不到的“意外”:

0 == "我爱你"; // 返回true
1 == "1 我爱你";// 返回true

  php教程里更有这样一组用于字符串比较的函数:strcmp,strcasecmp,strncasecmp(), strncmp(),他们都是如果前者比后者大,则返回大于0的整数;如果前者比后者小,则返回小于0的整数;如果两者相等,则返回0.他们比较的原理和其他语言的规则都是相同的。

strcmp是用于区分大小写(即大小写敏感)的字符串比较:
echo strcmp("abcdd", "abcde"); // 返回 1 (>0), 比较的是 "b"和"b"

strcasecmp用于不区分大小写的字符串比较:
echo strcasecmp("abcdd", "abcde"); // 返回 -1 (

strncmp用于比较字符串的一部分,从字符串的开头开始比较,第三个参数,为要比较的长度:
echo strncmp("abcdd", "abcde", 3); // 返回 1 (>0), 比较了 abc 和 abc

strncasecmp用于不区分大小写的比较字符串的一部分,从字符串的开头开始比较,第三个参数,为要比较的长度:
echo strncasecmp("abcdd", "abcde", 3); // 返回 0, 比较了 abc 和 abc, 由于不区分大小写,所以两者是相同的。

  更有一种情况是单单比较字符串大小,达不到我们预定的需求,比如照常理 10.gif 会比 5.gif 大,但如果应用上面几个函数,就会返回 -1,即表示 10.gif比5.gif,针对这种情况,php提供了两个自然对比的函数strnatcmp,strnatcasecmp:

echo strnatcmp("10.gif", "5.gif"); // 返回 1 (>0)
echo strnatcasecmp("10.gif", "5.gif"); // 返回 1 (>0)


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