Replace first two characters of a string in php

Question

I am dealing with a problem of time conversion from 12 hr format to 24 hour format.

Is there any single function in php to replace the first two characters of a string?

str_replace can be used only when I know the substring content to be replaced.

Answer 1

$str_to_replace = '12';

$input_str = 'ab345678';

$output_str = $str_to_replace . substr($input_str, 2);

echo $output_str;

"12345678"