How to change first occurrence of word in a string

问题

How do I do to change the first occurrence of a word in a string?

Example:

$a = "Yo! **Hello** this is the first word of Hello in this sentence";

$b = "Yo! **Welcome** this is the first word of Hello in this sentence";

回答1:

This works, although a bit inefficient:

$a = "Yo! **Hello** this is the first word of Hello in this sentence";
$a = preg_replace('/Hello/', 'Welcome', $a, 1);

The other popular answer:

$b = str_replace('Hello', 'Welcome', $a, 1);

does not work. The fourth argument of str_replace should be a variable, which is passed by reference and str_replace will set it to the number of replacements made.

A better solution would be to extract two sub-strings from the input string:

Sub-string before the first occurrence of Hello, call it $s1
Sub-string after the first occurrence of Hello, call it $s2

One can use the strpos to get the position.

Result is $s1.'Welcome'.$s2

回答2:

Just use substr twice with strpos.

$a = "Yo! **Hello** this is the first word of Hello in this sentence";
$search = "Hello";
$replacement = "Welcome";
$b = substr( $a, 0, strpos( $a, $search)) . $replacement . substr( $a, strpos( $a, $search) + strlen( $search));

Demo

回答3:

This is the best for compactness and performances:

if(($offset=strpos($string,$replaced))!==false){
   $string=substr_replace($replaced,$replacer,$offset,strlen($replaced));
}

Replace only the first occurrence without the overload of the regular expressions

回答4:

Use substr_replace().

回答5:

Use str_replace('Hello','Welcome',$a,1);

回答6:

Build It:

function str_replace_first($search, $replace, $source) {

  $explode = explode( $search, $source );
  $shift = array_shift( $explode );
  $implode = implode( $search, $explode );
  return $shift.$replace.$implode;

}

Call it:

$msg = "Yo! **Hello** this is the first word of Hello in this sentence";
echo str_replace_first( 'Hello', 'Welcome', $msg );

Try It:

http://sandbox.onlinephpfunctions.com/code/399ec70333832423c79d36a42032124d5c296d27

来源：https://stackoverflow.com/questions/8272108/how-to-change-first-occurrence-of-word-in-a-string

标签

php

string

replace