What's the term *ANSI C* specifies if it used with GNU89, C89, GNU99, C99?

Question

In Xcode IDE, I have an option to set C language dialect one of

• ANSI C
• GNU89
• C89
• GNU99
• C99
• Compiler Default

I understand what they mean except ANSI C. Because As I know, ANSI C is just one of C89 or C99. But there should be a reason about it's on there. What's the term ANSI C specifies in there?

Answer 1

edit Credit goes to @Nicholas Knight for posting a screenshot from XCode's C dialect selection window: http://dl.dropbox.com/u/14571816/xcodelang.png

ANSI C refers, historically, to the ANSI C89 standard (practically the same thing as C90). XCode uses a version of GCC as the compiler back-end for compiling C code, so I think that's where they get these 'options' from, as you can specify the -ansi flag or various std= flags to choose the mode the C compiler backend should operate in for compiling your code.

So if you pass it -ansi, and using the C compiler, it's equivalent to -std=c90, which is also equivalent to -std=c89 or -std=iso9899:1990.

-ansi

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

And if you use the -std flags, you can pass certain values to activate different language features.

-std=

Determine the language standard. This option is currently only supported when compiling C or C++.

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These arguments are equivalent:

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.

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These arguments are equivalent:

iso9899:199409 ISO C90 as modified in amendment 1.

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These following arguments are equivalent:

c99

c9x

iso9899:1999

iso9899:199x

ISO C99. Note that this standard is not yet fully supported; see http://gcc.gnu.org/gcc-4.5/c99status.html for more information. The names c9x and iso9899:199x are deprecated.

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These following arguments are equivalent:

gnu90

gnu89

GNU dialect of ISO C90 (including some C99 features). This is the default for C code.

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These following arguments are equivalent:

gnu99

gnu9x

GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC, this will become the default. The name gnu9x is deprecated.

Answer 2

Compilers have profiles of the languages they are targeting, like pmg said in his reply ANSI C was one of the earliest profiles, the one that is described in the K&R book.

The question of interest is, why do compilers maintain a list of legacy language profiles ? Because, writing code against the ANSI C profile is quite a strong guarantee that your code will work with virtually any compiler (more importantly compiler version).

When software projects claim ANSI-C compatibility they are telling you that it will compile everywhere give-or-take. Lua's source code is an example of this.