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 = 7;

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

    return num * multiplier;

};

printf("%d", myBlock(3));

// 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[3] = { "TomJohn", "George", "Charles Condomine" };

qsort_b(myCharacters, 3, sizeof(char *), ^(const void *l, const void *r) {

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

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

    return strncmp(left, right, 1);

});

// 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(0, [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",

                          @"Str?ng 21", // <-

                          @"Stri?g 21", // <-

                          @"String 02" ];

NSLocale *currentLocale = [NSLocale currentLocale];

__block NSUInteger orderedSameCount = 0;

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

    NSRange string1Range = NSMakeRange(0, [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

*/