NSString stringWithFormat的动态字符串格式 [英] dynamic string format with NSString stringWithFormat

问题描述

我一直在尝试制作动态字符串格式，以便通过用户选项精度或填充可以在某种程度上由用户定义。

I've been trying to make a dynamic string format so that through user options precision or padding could be somewhat user defined.

一个例子包括，以24小时时间格式填充前导零。在正常时间格式中，小时数可以用一个数字表示，也可以用零填充的数字表示。这以字符串格式表示：

An example includes, the padding of leading zeros as in the 24hour time format. In normal time format, the hours can be represented by a single digit, or a digit padded by a zero. This is represented in the string format:

...stringWithFormat:@"Hour: %02i", hour   // leading zero padded

和

...stringWithFormat:@"Hour: %i", hour     // not leading zero padded

我想要实现的是变量包含 @或 @02并在％和 i 之间的格式字符串中显示该变量。

What I would like to achieve is to have a variable containing either @"" or @"02" and have that variable presented in the format string between the % and the i.

我做了几个实验，似乎无法做到这一点，我开始认为用 stringWithFormat 。

I have done a couple of experiments and just can't seem to do this and am beginning to think that it's not possible with stringWithFormat.

我试过了：

... stringWithFormat：@小时： %% @ i，填充，小时

... stringWithFormat：@小时：％@％i ，填充，小时

和其他人。

任何想法？

推荐答案

有一种更好的方法可以做到这一点。

There's a better way to do this.

... stringWithFormat:@"Hour: %0*i", length, hour]; // note the asterisk

其中长度是你想要的位数。使用 1 获取无前导零，使用 2 根据需要获得前导零的长度为2。

where length is the number of digits you want. Use 1 to get no leading zeros, use 2 to get a length of 2 with leading zeros as needed.

仅供参考 - 要解决您最初尝试的问题，您需要分两步完成：

FYI - to solve what you originally tried you need to do it in two steps:

NSString *dynFmt = [NSString stringWithFormat:@"Hour: %%%@i", padding];
NSString *res = [NSString stringWithFormat:dynFmt, hour];

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