Question

很奇怪。我预计最后一个NSLog打印3但它不是

NSString *value = @"0(234)6";

NSRange beginParenthesis = [value rangeOfString:@"("];
NSRange endParenthesis = [value rangeOfString:@")"];

if (beginParenthesis.location != NSNotFound && endParenthesis.location != NSNotFound)
{
    NSLog(@"%ld", endParenthesis.location); // 5
    NSLog(@"%ld", beginParenthesis.location + 1); // 2
    NSLog(@"%ld", endParenthesis.location - beginParenthesis.location + 1); // 5?
}

我将beginParenthesis.location + 1保存到变量...它运作良好我预期...为什么？

NSRange beginParenthesis = [value rangeOfString:@"("];
NSRange endParenthesis = [value rangeOfString:@")"];

if (beginParenthesis.location != NSNotFound && endParenthesis.location != NSNotFound)
{
    NSInteger start = beginParenthesis.location + 1;
    NSLog(@"%ld", endParenthesis.location); //5
    NSLog(@"%ld", start); // 2
    NSLog(@"%ld", endParenthesis.location - start); // 3
}

论文之间有什么区别？

Answer 1

数学问题：

endParenthesis.location - beginParenthesis.location + 1给出u（5 - 1 + 1），即等于5。但是endParenthesis.location - start给出了5 - 2，即3。

所以你把括号括起来：

 NSLog(@"%ld", endParenthesis.location - (beginParenthesis.location + 1));

Answer 2

它被称为运算符优先级。请参阅here。

客观c - nsrange计算很奇怪

2 个答案: