cannot access __block variable of array type inside block
cannot access __block variable of array type inside block
- Subject: cannot access __block variable of array type inside block
- From: Jonathon Kuo <email@hidden>
- Date: Tue, 14 Dec 2010 19:30:32 -0800
I'm trying to learn GCD and reading http://developer.apple.com/library/mac/#featuredarticles/BlocksGCD/index.html
But the Global Concurrent Queues example in that document (last updated 2010-11-10) doesn't even compile. It complains about accessing array 'result' from within the block:
#define COUNT 128
__block double result[COUNT];
dispatch_apply(COUNT, q_default, ^(size_t i){
result[i] = complex_calculation(i); /* <=== ERROR HERE!
});
double sum = 0;
for (int i=0; i < COUNT; i++) sum += result[i];
What is wrong here? This looks like it should work. Below is my full program.
-Jonathon
#include <dispatch/dispatch.h>
#include <stdio.h>
#define COUNT 128
double complex_calculation( int i )
{
return i * 3.14;
}
int main()
{
int i = 0;
__block double result[COUNT];
dispatch_queue_t q_default;
/* get default queue */
q_default = dispatch_get_global_queue(0, 0);
dispatch_apply(COUNT, q_default, ^(size_t i) {
result[i] = complex_calculation(i); /* <=== ERROR HERE!
});
double sum = 0;
for (i=0; i < COUNT; i++) sum += result[i];
printf("%f\n", sum);
return 0;
}
$ cc -g blk3.c -o blk3
blk3.c: In function ‘__main_block_invoke_1’:
blk3.c:20: error: cannot access __block variable of array type inside block
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