gcc compile할 때 옵션 관련 질문드립니다...

man gcc

       -ansi  Support all ANSI standard C programs.

              This turns off certain features of GNU C that are incompatible with ANSI C, such  as  the  asm,
              inline  and  typeof keywords, and predefined macros such as unix and vax that identify the type
              of system you are using.  It also enables the undesirable and rarely used  ANSI  trigraph  fea-
              ture, and disallows `$' as part of identifiers.

              The  alternate  keywords __asm__, __extension__, __inline__ and __typeof__ continue to work de-
              spite `-ansi'.  You would not want to use them in an ANSI C program, of course, but it is  use-
              ful  to put them in header files that might be included in compilations done with `-ansi'.  Al-
              ternate predefined macros such as __unix__ and __vax__ are  also  available,  with  or  without
              `-ansi'.

              The  `-ansi'  option  does  not cause non-ANSI programs to be rejected gratuitously.  For that,
              `-pedantic' is required in addition to `-ansi'.

              The preprocessor predefines a macro __STRICT_ANSI__ when you  use  the  `-ansi'  option.   Some
              header  files  may  notice  this macro and refrain from declaring certain functions or defining
              certain macros that the ANSI standard doesn't call for; this is to avoid interfering  with  any
              programs that might use these names for other things.

       -pedantic
              Issue all the warnings demanded by strict ANSI standard C; reject all programs that use forbid-
              den extensions.

              Valid  ANSI  standard  C programs should compile properly with or without this option (though a
              rare few will require `-ansi').  However, without this option, certain GNU extensions and  tra-
              ditional  C  features are supported as well.  With this option, they are rejected.  There is no
              reason to use this option; it exists only to satisfy pedants.

              `-pedantic' does not cause warning messages for use of the alternate keywords whose names begin
              and end with `__'.  Pedantic warnings are also disabled in the expression that follows __exten-
              sion__.  However, only system header files should use these escape routes; application programs
              should avoid them.

       -Wall  All  of the above `-W' options combined.  These are all the options which pertain to usage that
              we recommend avoiding and that we believe is easy to avoid, even in conjunction with macros.

질문하시기 전에 man 페이지를 참고해주시기 바랍니다. :-)

ansi 옵션은 ANSI 표준으로 컴파일 하는거고 pedantic은 ANSI가 아닌 비표준 사양은 불평하는 메시지를 내라는 거고요.
Wall은 waning을 all 켜라는 겁니다. 컴파일 경고 메시지를 다 켜는 거죠.