Is this standard C

[Laserve]

Is the following code C99 code or does it happen to be an extension of my compiler? (gcc)

void func(void)
{
    int a[10] = { [4] = 1, [7] = 1 };
}

this is the same as:

void func(void)
{
    int a[10] = { 0, 0, 0, 0, 1, 0, 0, 1 };
}

[Dave Evans]

Is the following code C99 code or does it happen to be an extension of my compiler? (gcc)

void func(void)
{
    int a[10] = { [4] = 1, [7] = 1 };
}

this is the same as:

void func(void)
{
    int a[10] = { 0, 0, 0, 0, 1, 0, 0, 1 };
}

C99 Standard: yes
C89 Standard: no

Regards,

Dave

[Micko]

Yes,
This is example is from C99 standard
EXAMPLE 9 Arrays can be initialized to correspond to
the elements of an enumeration by using designators:

enum { member_one, member_two };
const char *nm[] = {
[member_two] = "member two",
[member_one] = "member one",
};

[coolshyam]

    int a[10] = { [4] = 1, [7] = 1 };

well well well well. the [4]=1 here refers to a[4]=1
and [7]=1 refers to a[7]=1.so they are one. but i couldnt understand how the remaining elements, a[0], a[1].....took zero as the default value.lemme check it out

[0rion]

C defaults to a value of 0 when you "attempt" to initialise it so to speak. Can't really explain it well but this code explains it a bit better:

#include <stdio.h>

int main(int argc, char **argv)
{
        int a[10] = { [4] = 1, [7] = 1 };
        int b[10] = { };
        int c[10];
        int i;

        for (i = 0; i < 10; i++)
        {
                printf("%d %d %d\n",a[i],b[i],c[i]);
        }

        return 0;
}

Notice how array "c" gets garbage values since we didn't initialise it at all, array "b" gets initialised to default 0 since we didn't specify what values we wanted. Array "a" also gets initialised to 0 unless specified, this causes the 5th and 8th cell of the array to hold a 1 due to our explicit initialisation.

[Jez]

I learn something new every day!

[quzah]

To explain it in simple terms, all uninitialized array memebers are set to zero. The only difference is where prior to C99, you could only do this:

int foo[10] = { 1, 2, 3 };

Which fills the first three elements, and zero fills the rest. In C99, you can set specific values to whatever you like.

int foo[10] = { 1, 2, 3, [1] = 5, [4] = 7 };

Giveing us an array containing:

{ 1, 5, 3, 0, 7, 0, 0, 0, 0, 0 }

Quzah.