块中访问C中的数组（可变数组数）的Objective-C [英] Access C Array within blocks (variable array count) Objective-C

问题描述

块是罚款，但有关编写C数组是什么？

Blocks are fine but what about writing C arrays?

鉴于这种情况的简化：

CGPoint points[10];
[myArray forEachElementWithBlock:^(int idx) {
    points[idx] = CGPointMake(10, 20); // error here
    // Cannot refer to declaration with an array type inside block
}];

在寻找了一段时间发现了这个可能的解决方案，把它在一个结构：

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);
}];

这会工作，但有一点限制我必须动态创建C数组：

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;

我如何能块内访问我的 CGPoint 阵列？

How can I access my CGPoint array within a block?

或

它甚至有可能在全部或我重写块方法来获得完整的功能？

Is it even possible at all or do I have to rewrite the block method to get the full functionality?

推荐答案

也许你可以在堆中分配的数组？

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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