??????????????????????????instr??substr??????????н????????????????????????????????????????????????????????
??????????substr?????????????????????????????????
????substr(string??start??length)
????????string??????????????????????????????
????start????????????????λ????????????????????????????????????????????????λ??????????????????????β?????λ??????0????????????е???????????????
????length??????????????????????????????? start ?????????λ????????????????????????????????????λ??????????????????
????????????
????substr("Hello World!"??2??1)???????e
????substr("Hello World!"??2)???????ello World!
????substr("Hello World!"??-2??1)???????d
????substr("Hello World!"??-2??-1)???????d!
????instr( string1?? string2?? start_position??nth_appearance ) ????????????????????????????е?λ?á?
????string1??????????????????в????
????string2???string1?в????????? ??
????start_position????????λ?á?
????nth_appearance????????????γ????string2. ????????????????????? 1.???????????????
????????????
????instr("Hello World!"??"o")???????5
????instr("Hello World!"??"o"??1??2)???????8????????￡???仰????"o"????????????λ??????????????“o”?????λ?á?
?????????????????????