The example is explained in the following illustration:

这个例子在下面的说面中得到了解释：

• myBlock 的返回值是int类型的 。
• 我们使用^声明了一个myBlock的block。
• 只需要一个参数，也是int类型的。
• 参数名是num。这是一个块的定义，
• 给myblock赋值。
• 这是block的主体。

Notice that the block is able to make use of variables from the same scope in which it was defined.

If you declare a block as a variable, you can then use it just as you would a function:

注意block可以使用定义在block定义作用用中的变量。

如果你把block定义成了一个变量，你可以像使用函数一样使用block。

 int multiplier = ;

 int (^myBlock)(int) = ^(int num) {

     return num * multiplier;

 };

 printf("%d", myBlock());

 // prints "21"

Using a Block Directly（直接使用block）

In many cases, you don’t need to declare block variables; instead you simply write a block literal inline where it’s required as an argument. The following example uses the qsort_b function. qsort_b is similar to the standard qsort_r function, but takes a block as its final argument.

在很多情况下你不需要把block定义成一个变量；相反的你可以直接写出一个block作为参数。下面的例子用到了qsort_b函数，qsort_b很类似标准的qsort_r函数，是指使用一个block作为一最后一个参数。

 char *myCharacters[] = { "TomJohn", "George", "Charles Condomine" };

 qsort_b(myCharacters, , sizeof(char *), ^(const void *l, const void *r) {

     char *left = *(char **)l;

     char *right = *(char **)r;

     return strncmp(left, right, );

 });

 // myCharacters is now { "Charles Condomine", "George", "TomJohn" }

Blocks with Cocoa（cocoa中的block）

Several methods in the Cocoa frameworks take a block as an argument, typically either to perform an operation on a collection of objects, or to use as a callback after an operation has finished. The following example shows how to use a block with the NSArray methodsortedArrayUsingComparator:. The method takes a single argument—the block. For illustration, in this case the block is defined as anNSComparator local variable:

Cocoa 框架中有一些方法使用block作为一个参数，特别是对多个对象进行操作，或者在一个操作结束之后回调。下面的例子展示了NSArray怎样在方法sortedArrayUsingComparator:中使用block。这个方法使用了一个参数——block。为了说明，这个block被定义为NSComparator类型的一个局部变量：

 NSArray *stringsArray = @[ @"string 1",

                            @"String 21",

                            @"string 12",

                            @"String 11",

                            @"String 02" ];

 static NSStringCompareOptions comparisonOptions = NSCaseInsensitiveSearch | NSNumericSearch |

         NSWidthInsensitiveSearch | NSForcedOrderingSearch;

 NSLocale *currentLocale = [NSLocale currentLocale];

 NSComparator finderSortBlock = ^(id string1, id string2) {

     NSRange string1Range = NSMakeRange(, [string1 length]);

     return [string1 compare:string2 options:comparisonOptions range:string1Range locale:currentLocale];

 };

 NSArray *finderSortArray = [stringsArray sortedArrayUsingComparator:finderSortBlock];

 NSLog(@"finderSortArray: %@", finderSortArray);

 /*

 Output:

 finderSortArray: (

     "string 1",

     "String 02",

     "String 11",

     "string 12",

     "String 21"

 )

 */

 NSArray *stringsArray = @[ @"string 1",

                           @"String 21", // <-

                           @"string 12",

                           @"String 11",

                           @"Strîng 21", // <-

                           @"Striñg 21", // <-

                           @"String 02" ];

 NSLocale *currentLocale = [NSLocale currentLocale];

 __block NSUInteger orderedSameCount = ;

 NSArray *diacriticInsensitiveSortArray = [stringsArray sortedArrayUsingComparator:^(id string1, id string2) {

     NSRange string1Range = NSMakeRange(, [string1 length]);

     NSComparisonResult comparisonResult = [string1 compare:string2 options:NSDiacriticInsensitiveSearch range:string1Range locale:currentLocale];

     if (comparisonResult == NSOrderedSame) {

         orderedSameCount++;

     }

     return comparisonResult;

 }];

 NSLog(@"diacriticInsensitiveSortArray: %@", diacriticInsensitiveSortArray);

 NSLog(@"orderedSameCount: %d", orderedSameCount);

 /*

 Output:

 diacriticInsensitiveSortArray: (

     "String 02",

     "string 1",

     "String 11",

     "string 12",

     "String 21",

     "Str\U00eeng 21",

     "Stri\U00f1g 21"

 )

 orderedSameCount: 2

 */