Thread: Any problem with casting like this: (char[]){0,1,2,3,4)?

I was getting "excess elements in scalar initializer" errors from GCC from the following code, even though it still compiled and ran fine:

Code:

void *array[] = {
	(char){0,1,2,3,4},
	(char){5,6,7,8,9}
};

I was able to get rid of the warnings by doing this:

Code:

void *array[] = {
	(char[]){0,1,2,3,4},
	(char[]){5,6,7,8,9}
};

Is this just because I'm informing GCC that I the data should be initialized as an array? Again, the previous code worked even with the warnings.

Anything I should be worried about?

the second one looks ok according to the GCC manual for that nonstandard extension. the first one says 'you told me the next value is a char, but you gave me an array initializer'

I find it hard to believe that the first one would run fine if you tried to access the elements.

Try printing the elements: surely this crashes?

Code:

   for (i = 0; i < 2; i++)
   {
       char*  arr = array[i];
       printf("\n");
       for (j = 0; j < 5; j++)
       {
          printf("%d ", arr[j]);          
       }
   }

Your char cast tells GCC to turn 0,1,2,3,4 into a single char. It doesn't matter that this value will then be converted to a void*, it's no more sensible than doing:

Code:

 char c = {0,1,2,3,4};

The GCC I tried this on took the first value and ignored the rest, then interpreted that char as a pointer (with a warning: "initialization makes pointer from integer without a cast"). Don't know if all GCCs behave the same.

That's the equivalent of:

Code:

void *array[] = {
    (void*)0,
    (void*)5
};

Which is definitely not what you want.

So yes, you should be worried whenever you see this warning. It's pretty annoying that this is a warning rather than an error...

Originally Posted by dmh2000

the second one looks ok according to the GCC manual for that nonstandard extension.

Is it nonstardard? I think it's C99.

Originally Posted by smokeyangel

I find it hard to believe that the first one would run fine if you tried to access the elements.

Try printing the elements: surely this crashes?

Actually yes, it does. Sorry, that was a bad example. The example I should have used was in fact a struct:

Code:

struct test{
	char a[5];
	char b[5];
} test;

memcpy(&test, &((struct test){0,1,2,3,4,5,6,7,8,9}), sizeof(struct test));

That was giving me a warning in GCC even though the code compiled and ran. I realized, however, that I made a mistake and should have done this instead:

Code:

memcpy(&test, &((struct test){{0,1,2,3,4},{5,6,7,8,9}}), sizeof(struct test));

Originally Posted by Click_here

Is this the sort of thing that you are after?

Code:

    char arr1[5] = {0,1,2,3,4};
    char arr2[5] = {5,6,7,8,9};
    void *array[] = {arr1, arr2};


    int i,j;
    for (i = 0; i < 2; i++)
    {
        char (*s_array)[5] = array[i];


        printf("\n");
        for (j = 0; j < 5; j++)
        {
           printf("%d ", (*s_array)[j]);
        }
    }

I was hoping to avoid having to first initialize each "secondary" array individually, then initialize the pointer array with the secondary arrays, if that makes sense.

Anyway, I found this:

Using the GNU Compiler Collection (GCC)

Apparently the (char[]) cast is valid C99. I compiled my code in both GCC and Clang, and got no warnings.

I'm using GCC 4.7.2 and Apple's Clang/LLVM 3.1.