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

Question

Hi,

-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.

Text above is extract from this note. First thing first, what is the purpose of usage of -pedantic and -ansi option with GCC/G++ compiler, I couldn't understand the above description. Can anyone tell me the circumstances of using the above two options? When should I use it? Is it important one?

THanks @!

Answer 1

If your code needs to be portable then you can test that it compiles without any gcc extensions or other non-standard features. If your code compiles with -pedantic -ansi then in theory it should compile OK with any other ANSI standard compiler.

Answer 2

If you're writing code that you envisage is going to be compiled on a wide variety of platforms, with a number of different compilers, then using these flags yourself will help to ensure you don't produce code that only compiles under GCC.

Answer 3

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.

Answer 4

Basically, it will make your code a lot easier to compile under other compilers which also implement the ANSI standard, and, if you are careful in which libraries/api calls you use, under other operating systems/platforms.

The first one, turns off SPECIFIC features of GCC. (-ansi) The second one, will complain about ANYTHING at all that does not adhere to the standard (not only specific features of GCC, but your constructs too.) (-pedantic).

Answer 5

Pedantic makes it so that the gcc compiler rejects all GNU C extensions not just the ones that make it ANSI compatible.