来自double的objective-c stringvalue

Question

我有以下代码：

double d1 = 12.123456789012345;

NSString *test1 = [NSString stringWithFormat:@"%f", d1]; // string is: 12.123457

NSString *test1 = [NSString stringWithFormat:@"%g", d1]; // string is: 12.1235

如何获得与d1完全相同的字符串值？

Answer 1

可以帮助您查看Apple的String Format Specifiers指南。

%f  64-bit floating-point number 
%g  64-bit floating-point number (double), printed in the style of %e if the exponent is less than –4 or greater than or equal to the precision, in the style of %f otherwise

同时阅读floating point (in)accuracy，当然还有What Every Computer Scientist Should Know About Floating-Point Arithmetic。

如果您确实希望字符串与双精度匹配，请使用NSString对其进行编码，并在需要值时调用doubleValue。另请查看NSNumberFormatter。

Answer 2

怎么样

NSString *test1 = [NSString stringWithFormat:@"%.15f", d1];

或者只是选择双击

NSString *test1 = [NSString stringWithFormat:@"%lf", d1];