Objective-C隐式转换将整数精度'NSUInteger'(aka'unsigned long')转换为'int'警告

问题描述

我正在做一些练习，并且收到警告，指出:

I'm working through some exercises and have got a warning that states:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{
    @autoreleasepool {

        NSArray *myColors;

        int i;
        int count;

        myColors = @[@"Red", @"Green", @"Blue", @"Yellow"];

        count = myColors.count; //  <<< issue warning here

        for (i = 0; i < count; i++)

        NSLog (@"Element %i = %@", i, [myColors objectAtIndex: i]);
    }

    return 0;
}

推荐答案

NSArray的count方法返回NSUInteger，并且在64位OS X平台上

The count method of NSArray returns an NSUInteger, and on the 64-bit OS X platform

• NSUInteger定义为unsigned long，并且
• unsigned long是64位无符号整数.
• int是32位整数.

• NSUInteger is defined as unsigned long, and
• unsigned long is a 64-bit unsigned integer.
• int is a 32-bit integer.

因此int的数据类型比NSUInteger小，因此是编译器警告.

So int is a "smaller" datatype than NSUInteger, therefore the compiler warning.

另请参见:

要解决该编译器警告，可以将本地count变量声明为

To fix that compiler warning, you can either declare the local count variable as

NSUInteger count;

或(如果您确定数组不会包含超过2^31-1个元素！)，添加一个明确的演员表:

or (if you are sure that your array will never contain more than 2^31-1 elements!),add an explicit cast:

int count = (int)[myColors count];

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