declaring integer array in objective c without NSArray.n

Question

(Question updated after first comment)

int max_size = 20; int h[max_size];

Debugging gives a value of [-1] for h when using max_size to initialize;

If instead I initialize using an integer. So the code is:int h[20] , it works fine.

This was with GCC 4.2 on Mac OS X 10.6.

Works for me. It might help if you reduce it to a simple test case and update your question to include that code so we can see specifically what's going wrong. — Chuck
– Chuck, Commented Sep 27, 2010 at 22:14
+1 @Chuck. Anything you can do in C you can do in Objective-C. — Carl Norum
– Carl Norum, Commented Sep 27, 2010 at 22:39
Where are you declaring your array? Inside a method/function? Or in the global scope? And what exactly is -1 according to the debugger? — anon
– anon, Commented Sep 28, 2010 at 11:03
All the code is written in the same function scope. h[0] or h[max_size] gives -1. I'm using GCC 4.2 as a compiler. — stone
– stone, Commented Sep 29, 2010 at 19:59

Chuck · Accepted Answer · 2010-09-27 23:18:11Z

2

I just compiled and ran the following program incorporating your code:

#import <Foundation/Foundation.h>

int main() {
    int max_size = 20;
    int h[max_size];

    h[0] = 5;
    NSLog(@"It is %d", h[0]);

    return 0;
}

It worked fine. The problem is something besides simply declaring an array.

This was with GCC 4.0.1 on Mac OS X 10.4.

answered Sep 27, 2010 at 23:18

Chuck

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2 Comments

stone Over a year ago

My complier is GCC 4.2 on Mac OS X 10.6. And if I change it to LLVM GCC 4.2, then it works fine, but I don't see the variable in my debugger window. I don't even know what LLVM is. There must be an alternate solution.

MrTJ Over a year ago

In this case the compiler knows that max_size can not be changed between the first two lines of your function thus it can decide the size if the h array at compile time. Your code will not work if the value of max_size is calculated in a more complicated way.

Sam · Accepted Answer · 2010-09-27 23:08:47Z

0

If I recall correctly, some compilers need to know the size of stack-allocated arrays explicitly at compile-time. This (possibly) being the case, you could make your max_size variable const or an #define macro (or an integer literal, as you've done.) Alternatively, you could dynamically allocate the array and then the size could be any-old variable

ex:

int *array = calloc(max_size, sizeof(int));

answered Sep 27, 2010 at 23:08

Sam

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2 Comments

Chuck Over a year ago

This is not the case for GCC, and when it is the case, a compiler that doesn't support that feature will normally flag the declaration as an error rather than silently compiling nonsense.

Sam Over a year ago

Ah, that shows some ignorance on my part. Thanks for the correction.

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