c - iOS 中标志结构的用途是什么？

Question

struct
{
    unsigned resizesCellWidths:1;
    unsigned numColumns:6;
    unsigned separatorStyle:3;
    unsigned allowsSelection:1;
    unsigned backgroundViewExtendsUp:1;
    unsigned backgroundViewExtendsDown:1;
    unsigned usesPagedHorizontalScrolling:1;
    unsigned updating:1;
    unsigned ignoreTouchSelect:1;
    unsigned needsReload:1;
    unsigned allCellsNeedLayout:1;
    unsigned isRotating:1;
    unsigned clipsContentWidthToBounds:1;
    unsigned isAnimatingUpdates:1;
    unsigned requiresSelection:1;
    unsigned contentSizeFillsBounds:1;
    unsigned delegateWillDisplayCell:1;
    unsigned delegateWillSelectItem:1;
    unsigned delegateWillSelectItemMultiTouch:1;
    unsigned delegateWillDeselectItem:1;
    unsigned delegateDidSelectItem:1;
    unsigned delegateDidSelectItemMultiTouch:1;
    unsigned delegateDidDeselectItem:1;
    unsigned delegateGestureRecognizerActivated:1;
    unsigned delegateAdjustGridCellFrame:1;
    unsigned delegateDidEndUpdateAnimation:1;
    unsigned dataSourceGridCellSize:1;
    unsigned int isEditing:1;
    unsigned __RESERVED__:1;
} _flags;

1. 这个结构的目的是什么？
2. 每行末尾的 :1 符号表示什么？
3. 当没有显式类型时，unsigned 修饰符的含义是什么？

谢谢

Answer 1

那些是 bitfields .由于其中大部分是标志，它们只有 2 个可能的值，因此无需为每个字段分配超过 1 位。 (该结构中有几个异常(exception))

unsigned 可以作为一种类型独立存在。它只是一个 unsigned int。