PHP inserts a string at the specified position of the string

Php inserts a string into a string at the specified position of the string ** @ paramstring $ str # string to be processed * @ paramint $ I # insert position * @ paramstring $ substr # string to be inserted * functionstr_insert ($ str, $ I, $ substr) {for ($ j0; $ j & lt; php inserts a string at a specified position in the string

// Insert a string/** @ param string $ str # string to be processed * @ param int $ I # insert position * @ param string $ substr # string to be inserted */function str_insert ($ str, $ I, $ substr) {for ($ j = 0; $ j <$ I; $ j ++) {$ startstr. = $ str [$ j];} for ($ j = $ I; $ j