Ordered Array Initialization Syntax in C

Question

I came across an unfamiliar array initialization syntax in the code of xv6. Original code is in syscall.s

static int (*syscalls[])(void) = {
[SYS_fork]    sys_fork,
[SYS_exit]    sys_exit,
[SYS_wait]    sys_wait,
// ...
[SYS_halt]  sys_halt,
};

I ran my sample code to confirm this

const char* mystrings[] = {
   [2] "this",
   [1] "is",
   [0] "cool",
};


int main (int argc, char const* argv[])
{
   printf("%s %s %s\n",mystrings[0],mystrings[1],mystrings[2]);

        return 0;
}

Output was

cool is this

What is this kind of array initialization in C code? Where can i ( find documentation for this? ( I compiled with gcc 4.6.3 )

Kerrek SB · Accepted Answer · 2014-04-02 14:11:18Z

3

Designated initializers, part of C99. See for example the GCC documentation. The current standard reference is C11 6.7.9.

However, GCC offers a few extensions to this syntax, such as omitting the = sign, or ranges.

edited Apr 2, 2014 at 14:11

answered Apr 2, 2014 at 14:05

Kerrek SB

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1 Comment

Kerrek SB Over a year ago

@ShafikYaghmour: Well spotted, thanks a lot! I incorporated that in the post.

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