int mb_strpos ( 
  string $haystack , 
  string $needle [, 
  int $offset = 0 [, 
  string $encoding = mb_internal_encoding() ]] 
  )
//Finds position of the first occurrence of a string in a string.
// 查找 string 在一个 string 中首次出现的位置。

//Performs a multi-byte safe strpos() operation based on number of characters. The first character's position is 0, the second character position is 1, and so on.
// 基于字符数执行一个多字节安全的 strpos() 操作。 第一个字符的位置是 0，第二个字符的位置是 1，以此类推。

?php
/**
 * Created by PhpStorm.
 * User: zhangrongxiang
 * Date: 2018/2/2
 * Time: 下午11:16
 */

$str = "Hello World! Hello PHP";
$pos = mb_strpos( $str, "Hello", 0, mb_internal_encoding() );
echo $pos . PHP_EOL;//0
$pos = mb_strpos( $str, "Hello", 2, mb_internal_encoding() );
echo $pos . PHP_EOL;//13

function mb_str_replace( $haystack, $search, $replace, $offset = 0, $encoding = 'auto' ) {
  $len_sch = mb_strlen( $search, $encoding );
  $len_rep = mb_strlen( $replace, $encoding );
  
  while ( ( $offset = mb_strpos( $haystack, $search, $offset, $encoding ) ) !== false ) {
    $haystack = mb_substr( $haystack, 0, $offset, $encoding )
          . $replace
          . mb_substr( $haystack, $offset + $len_sch,
        $le = mb_strlen( $haystack ) - mb_strlen( $search ) + mb_strlen( $replace ),
        $encoding );
    //echo $le.PHP_EOL;
    $offset = $offset + $len_rep;
    if ( $offset > mb_strlen( $haystack, $encoding ) ) {
      break;
    }
  }
  
  return $haystack;
}

$replace = mb_str_replace( "hello world !hello world !hello world !hello world !", "hello", "hi" );
echo $replace . PHP_EOL; //hi world !hi world !hi world !hi world !

//hi PHP !hi PHP !hi PHP !hi PHP !
echo mb_str_replace( $replace, "world", "PHP" ) . PHP_EOL;
echo mb_str_replace( $replace, " ", "-" ) . PHP_EOL;

//PHP是世界上最好的语言😂😂😂😂😂😂
echo mb_str_replace( "PHP是世界上最好的语言😄😄😄😄😄😄", '😄', '😂', 0, mb_internal_encoding() ) . PHP_EOL;
echo mb_str_replace( "112233445566", '22', '00' ) . PHP_EOL;//110033445566
echo mb_str_replace( '😄😄😄😄', '😄', '😫1', 2, mb_internal_encoding() ) . PHP_EOL;
echo mb_str_replace( '1111', '111', '0', 1 ) . PHP_EOL;//10
echo mb_strlen( '😄😄😄😄' ) . PHP_EOL;//4

//代码开发代码
echo mb_str_replace( '软件开发软件', '软件', '代码' ,0,mb_internal_encoding()) . PHP_EOL;
//代码开发 //todo??
echo mb_str_replace( '软件开发软件', '软件', '代码' ) . PHP_EOL;