gcc 특정 표준 따르도록 강제하기

-ansi

In C mode, this is equivalent to -std=c90. In C++ mode, it is equivalent to -std=c++98.

-std=

A value for this option must be provided; possible values are

‘c90’

‘c89’

‘iso9899:1990’

Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90 are disabled). Same as -ansi for C code. 

‘iso9899:199409’

ISO C90 as modified in amendment 1. 

‘c99’

‘c9x’

[링크 : https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html]