why a[i] is not compiling . array compilation error

[nkrao123@gmail.]

Hi,

i tried to compile the below program

1st program

int main()
{
        int i=10;
        int a[2]={i,i+1};
        printf ("hai %d\n",a[0]);
        return 0;
}

2nd program

int main()
{
        int i=10;
        int j=2;
        int a[j]={i,i+1};
        printf ("hai %d\n",a[0]);
        return 0;
}

Why i am able to compile first program and getting compile error for second program?

[laserlight]

Unless you are able to make use of the variable length array feature introduced in the 1999 edition of the C standard, your array a must have a fixed size known at compile time, so j cannot be a variable.

[quzah]

Unless you are able to make use of the variable length array feature introduced in the 1999 edition of the C standard, your array a must have a fixed size known at compile time, so j cannot be a variable.

Translation: You are still using Turbo C!


Quzah.

[nkrao123@gmail.]

Hi,

is it variable length array features is compiler dependent?

I am using the gcc compiler version (gcc (GCC) 3.4.5 20051201 (Red Hat 3.4.5-2)). my compiler will support variable length array feature?

can you let me know small c program with variable length array feature?

[Subsonics]

You can compile with compile flag: -std=c99

[laserlight]

is it variable length array features is compiler dependent?

In theory, no. In practice, yes, because not all C compilers in present use conform sufficiently to C99.

I am using the gcc compiler version (gcc (GCC) 3.4.5 20051201 (Red Hat 3.4.5-2)). my compiler will support variable length array feature?

It should. You may need to pass -std=c99 as a compiler option.

can you let me know small c program with variable length array feature?

Your second program is such an example program, except that you cannot initialise the array like that. Oh and remember to #include <stdio.h>.

[MK27]

Newer versions of gcc let this slide with a warning. I didn't start C programming until after gcc 4.+ was released, so I'm guessing that 3.4.5 does not do that. Try compiling:

gcc -Wall -std=c99

You can also use "-std=gnu99" which might be slightly more compatible with the default on linux (std=gnu89).

If that doesn't work, post the actual error you are getting.

[nkrao123@gmail.]

HI light and Mk27,

i am getting error if i compile with "gcc name.c -std=c99" and "gcc name.c -std=gnu99"

error

gcc 22.c -std=gnu99
22.c: In function `main':
22.c:6: error: variable-sized object may not be initialized
22.c:6: warning: excess elements in array initializer
22.c:6: warning: (near initialization for `a')
22.c:6: warning: excess elements in array initializer
22.c:6: warning: (near initialization for `a')



gcc 22.c -std=c99
22.c: In function `main':
22.c:6: error: variable-sized object may not be initialized
22.c:6: warning: excess elements in array initializer
22.c:6: warning: (near initialization for `a')
22.c:6: warning: excess elements in array initializer
22.c:6: warning: (near initialization for `a')




i fell my compiler may not support this feature. am i right?

[laserlight]

I told you precisely what you did wrong: "except that you cannot initialise the array like that", as did your compiler: "variable-sized object may not be initialized".

[quzah]

22.c:6: error: variable-sized object may not be initialized

Try actually reading the error message. Also try reading what people actually write to you:

I told you precisely what you did wrong

^ See that?


Quzah.

[nkrao123@gmail.]

It should. You may need to pass -std=c99 as a compiler option.

Light used that word as it should. I thought my compiler may have that features. That why i tried. Now i understand that my compilr does not supporting this feature

[quzah]

Now i understand that my compilr does not supporting this feature

No, no you don't. You don't understand at all, because you aren't reading what people are telling you over and over.


Quzah.

[laserlight]

Light used that word as it should. I thought my compiler may have that features. That why i tried. Now i understand that my compilr does not supporting this feature

You misunderstand because you jumped to a conclusion without reading the rest of what I wrote. Try this program:

#include <stdio.h>

int main(void)
{
    size_t n = 10;
    int numbers[n];

    for (size_t i = 0; i < n; ++i)
    {
        numbers[i] = i * 2;
    }

    for (size_t i = 0; i < n; ++i)
    {
        printf("%d\n", numbers[i]);
    }

    return 0;
}

There is no need for numbers to be a variable length array in the above program, but perhaps the value of n could have been obtained from input instead.

Now, this program should compile, once you add braces for the main function:

int main(void)
return 0;

Attempt to compile it. Compilation fails. You can thus jump to the conclusion that your C compiler does not support compiling even such a trivial C program

[MK27]

Light used that word as it should. I thought my compiler may have that features. That why i tried. Now i understand that my compilr does not supporting this feature

Sorry, partially my mistake. As per laserlight's post above, what c99 will allow is this:

int array[x];

Where x may be determined at runtime. Which means you cannot initialize it to any value, ie.

int array[x] = {1, 2, 3};

is no good. You can use a "variable-sized object" but you can't initialize it in the declaration.

[quzah]

And because you still won't understand what they're saying:

Which means you cannot initialize it to any value, ie.

int array[x] = {1, 2, 3};

is no good. You can use a "variable-sized object" but you can't initialize it in the declaration.

You can do what is in green.
You can't do the part in red.


Quzah.