Access C Array within blocks (variable array count) Objective-C
Blocks are fine but what about writing C arrays?
Given this simplified situation:
CGPoint points[10];
[myArray forEachElementWithBlock:^(int idx) {
points[idx] = CGPointMake(10, 20); //开发者_Python百科 error here
// Cannot refer to declaration with an array type inside block
}];
after searching a while found this possible solution, to put it in a struct:
__block struct {
CGPoint points[100];
} pointStruct;
[myArray forEachElementWithBlock:^(int idx) {
pointStruct.points[idx] = CGPointMake(10, 20);
}];
this would work but there is a little limitation I have to create the c array dynamically:
int count = [str countOccurencesOfString:@";"];
__block struct {
CGPoint points[count]; // error here
// Fields must have a constant size: 'variable length array in structure' extension will never be supported
} pointStruct;
How can I access my CGPoint
array within a block
?
OR
Is it even possible at all or do I have to rewrite the block method to get the full functionality?
Another simple answer which works for me is the following:
CGPoint points[10], *pointsPtr;
pointsPtr = points;
[myArray forEachElementWithBlock:^(int idx) {
pointsPtr[idx] = CGPointMake(10, 20);
}];
Maybe you can allocate the array on the heap?
// Allocates a plain C array on the heap. The array will have
// [myArray count] items, each sized to fit a CGPoint.
CGPoint *points = calloc([myArray count], sizeof(CGPoint));
// Make sure the allocation succeded, you might want to insert
// some more graceful error handling here.
NSParameterAssert(points != NULL);
// Loop over myArray, doing whatever you want
[myArray forEachElementWithBlock:^(int idx) {
points[idx] = …;
}];
// Free the memory taken by the C array. Of course you might
// want to do something else with the array, otherwise this
// excercise does not make much sense :)
free(points), points = NULL;
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