What is the purpose of using -pedantic in GCC/G++ compiler?

Question

This note says:

-ansi: tells the compiler to implement the ANSI language option. This turns off certain "features" of GCC which are incompatible with the ANSI standard.

-pedantic: used in conjunction with -ansi, this tells the compiler to be adhere strictly to the ANSI standard, rejecting any code which is not compliant.

First things first:

• What is the purpose of the -pedantic and -ansi options of the GCC/G++ compiler (I couldn't understand the above description)?
• Can anyone tell me the right circumstances for using these two options?
• When should I use them?
• Are they important?

Answer 1

I use it all the time in my coding.

The -ansi flag is equivalent to -std=c89. As noted, it turns off some extensions of GCC. Adding -pedantic turns off more extensions and generates more warnings. For example, if you have a string literal longer than 509 characters, then -pedantic warns about that because it exceeds the minimum limit required by the C89 standard. That is, every C89 compiler must accept strings of length 509; they are permitted to accept longer, but if you are being pedantic, it is not portable to use longer strings, even though a compiler is permitted to accept longer strings and, without the pedantic warnings, GCC will accept them too.