Which most common extensions are there (or used) to ANSI C?

StackOverflow https://stackoverflow.com/questions/1829824

Question

You can put a link to comparison matrix or lists of extensions available to main compilers. If none of this is available, you could write a list of extension you use or like in your favorite compiler.

OTHER TIPS

C++/ISO-C style comments by far: //

Well, this depends on whether you mean C89 or C99 when you say "ANSI C". Since most mainstream implementations aren't fully C99-compliant yet, I'm going to assume C89.

In that case, I'd say (and not including specific APIs like POSIX or BSD Sockets):

  • long long must be the most common extension;
  • followed by allowing accesses to union members other than the last written;
  • inline is probably up there;
  • snprintf is available in a lot of places;
  • allowing casting between function pointers and void pointers is widespread;
  • alloca

Edit: Ahh yes, how could I forget the ubiquitous // style comment.

In one of the notorious compilers for embedded C, you can specify little- or big-endian for a struct type independently from the processor's preference. Very convenient for writing device drivers, if you remember not to access one of the fields through (say) an int* that forgets the endianness.

Are you serious with the feature matrix thing? Do you think SO members have nothing better to do?

A number of compilers allow anonymous structs inside anonymous unions, which is useful for some things, e.g.:

struct vector3
{
    union
    {
        struct
        {
            float x, y, z;
        };
        float v[3];
    };
};

// members can now be accessed by name or by index:
vector3 v;
v.x = 1.0f; v.y = 2.0f; v.z = 3.0f;
v.v[0] = v.v[1] = v.v[2] = 0.0f;
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