How to implement partial replacement in PHP

How to implement partial replacement in PHP: 1. Implement partial replacement through the "substr_replace" function; 2. Implement partial replacement through the self-made asterisk replacement function "replaceStar($str, $start, $length=0)" replace.

The operating environment of this article: windows7 system, PHP7.1 version, DELL G3 computer

PHP realizes partial replacement, uses PHP to Replace part of the content with asterisks

In a recent project, I encountered the need to hide the middle digits of someone’s mobile phone number and only display the last 4 digits of their ID number. At the beginning, I searched online and saw that someone used the substr_replace function to replace it. I also used this function later, but it was not very useful when I used it.

1. substr_replace

Let’s first look at the syntax of this function:

The code is as follows:

substr_replace(string,replacement,start,length)

Parameters	Description
##string	Required. Specifies the string to check.
replacement	Required. Specifies the string to be inserted.
start	Required. Specifies where in the string to begin replacement. Positive numbers - Start replacing at the start offset Negative numbers- Replace #start th offset from the end of the string 0 - within the string Start replacing
charlist	at the first character. Optional. Specifies how many characters to replace. Positive number - the length of the string to be replaced Negative number - the number of characters to be replaced from the end of the string 　0 - Insert instead of replacing

• 当start与charlist都为正数的时候，非常好理解，也很符号人的逻辑，start是从0开始的，如下图，根据条件，绿色的将是要被替换的元素

• 当start为负数，charlist为正数的时候，也挺好理解的

• 当start为正数，charlist为负数的时候，这个我一开始理解错了

• 当start为负数，charlist为负数的时候，有一个地方需要注意的就是：如果 start 是负数且 length 小于等于 start，则 length 为 0。这个坑挺容易踩到的

• charlist为0的时候，就变成插入了，而不是替换，额。。。

用下来，我是感觉不是很顺手，虽然说满足我现在的需求还是可以的，但是如果将来需要一些扩展的话，耍起来挺吃力的，所以就想到自己构造一个，将来用起来也方便。

推荐学习：《PHP视频教程》

二、自制的星号替换函数

代码如下:

replaceStar($str, $start, $length = 0)

前面的两个参数与上面的一样，最后的参数与上面不同

• 当start与length都为正数，与substr_replace表现的一样

• 当start为负数，length为正数，与substr_replace表现的一样

源码分享

public static function replaceStar($str, $start, $length = 0)
{
 $i = 0;
 $star = '';
 if($start >= 0) {
  if($length > 0) {
  $str_len = strlen($str);
  $count = $length;
  if($start >= $str_len) {//当开始的下标大于字符串长度的时候，就不做替换了
   $count = 0;
  }
  }elseif($length < 0){
  $str_len = strlen($str);
  $count = abs($length);
  if($start >= $str_len) {//当开始的下标大于字符串长度的时候，由于是反向的，就从最后那个字符的下标开始
   $start = $str_len - 1;
  }
  $offset = $start - $count + 1;//起点下标减去数量，计算偏移量
  $count = $offset >= 0 ? abs($length) : ($start + 1);//偏移量大于等于0说明没有超过最左边，小于0了说明超过了最左边，就用起点到最左边的长度
  $start = $offset >= 0 ? $offset : 0;//从最左边或左边的某个位置开始
  }else {
  $str_len = strlen($str);
  $count = $str_len - $start;//计算要替换的数量
  }
 }else {
  if($length > 0) {
  $offset = abs($start);
  $count = $offset >= $length ? $length : $offset;//大于等于长度的时候 没有超出最右边
  }elseif($length < 0){
  $str_len = strlen($str);
  $end = $str_len + $start;//计算偏移的结尾值
  $offset = abs($start + $length) - 1;//计算偏移量，由于都是负数就加起来
  $start = $str_len - $offset;//计算起点值
  $start = $start >= 0 ? $start : 0;
  $count = $end - $start + 1;
  }else {
  $str_len = strlen($str);
  $count = $str_len + $start + 1;//计算需要偏移的长度
  $start = 0;
  }
 }

 while ($i < $count) {
  $star .= &#39;*&#39;;
  $i++;
 }

 return substr_replace($str, $star, $start, $count);
}

不擅长算法，这里就用很普通的逻辑来展示啦，没有用到啥数学公式。

• if($start >= 0)这里做start大于等于0与小于0的分支

• 在start 的分之中，分别再做length 大于0，小于0和等于0的三个分支

• 最后计算出start、count和要替换的星号字符串，最后计算出的start与count都是正数，运用substr_replace做替换

单元测试

public function testReplaceStar()
 {
 $actual = App_Util_String::replaceStar('123456789', 3, 2);
 $this->assertEquals($actual, '123**6789');
 
 $actual = App_Util_String::replaceStar('123456789', 9);
 $this->assertEquals($actual, '123456789');
 
 $actual = App_Util_String::replaceStar('123456789', 9, 2);
 $this->assertEquals($actual, '123456789');
 
 $actual = App_Util_String::replaceStar('123456789', 9, -9);
 $this->assertEquals($actual, '*********');
 
 $actual = App_Util_String::replaceStar('123456789', 9, -10);
 $this->assertEquals($actual, '*********');
 
 $actual = App_Util_String::replaceStar('123456789', 9, -11);
 $this->assertEquals($actual, '*********');
 
 $actual = App_Util_String::replaceStar('123456789', 3);
 $this->assertEquals($actual, '123******');
 
 $actual = App_Util_String::replaceStar('123456789', 0);
 $this->assertEquals($actual, '*********');
 
 $actual = App_Util_String::replaceStar('123456789', 0, 2);
 $this->assertEquals($actual, '**3456789');

 $actual = App_Util_String::replaceStar('123456789', 3, -3);
 $this->assertEquals($actual, '1***56789');
 
 $actual = App_Util_String::replaceStar('123456789', 1, -5);
 $this->assertEquals($actual, '**3456789');
 
 $actual = App_Util_String::replaceStar('123456789', 3, -3);
 $this->assertEquals($actual, '1***56789');
 
 $actual = App_Util_String::replaceStar('123456789', -3, 2);
 $this->assertEquals($actual, '123456**9');
 
 $actual = App_Util_String::replaceStar('123456789', -3, 5);
 $this->assertEquals($actual, '123456***');
 
 $actual = App_Util_String::replaceStar('123456789', -1, 2);
 $this->assertEquals($actual, '12345678*');
 
 $actual = App_Util_String::replaceStar('123456789', -1, -2);
 $this->assertEquals($actual, '1234567**');
 
 $actual = App_Util_String::replaceStar('123456789', -4, -7);
 $this->assertEquals($actual, '******789');
 
 $actual = App_Util_String::replaceStar('123456789', -1, -3);
 $this->assertEquals($actual, '123456***');
 
 $actual = App_Util_String::replaceStar('123456789', -1);
 $this->assertEquals($actual, '*********');
 
 $actual = App_Util_String::replaceStar('123456789', -2);
 $this->assertEquals($actual, '********9');
 
 $actual = App_Util_String::replaceStar('123456789', -9);
 $this->assertEquals($actual, '*23456789');
 
 $actual = App_Util_String::replaceStar('123456789', -10);
 $this->assertEquals($actual, '123456789');
 
 $actual = App_Util_String::replaceStar('123456789', -10, -2);
 $this->assertEquals($actual, '123456789');
 }

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