4 ms·

My contribution to an example of something done right in the first FORTRAN and then done wrong many times afterwards: "The March of Progress > * 1956: Fortran

by acqq 7y ago

My contribution to an example of something done right in the first FORTRAN and then done wrong many times afterwards: "The March of Progress > * 1956: Fortran I: > PRINT 1, X > 1 FORMAT (F10.2) * 1980: C printf("%10.2f", x); * 1988: C++ cout << setw(10) << setprecision(2) << showpoint << x; * 1996: Java java.text.NumberFormat formatter = java.text.NumberFormat.getNumberInstance(); formatter.setMinimumFractionDigits(2); formatter.setMaximumFractionDigits(2); String s = formatter.format(x); for (int i = s.length(); i < 10; i++) System.out.print(' '); System.out.print(s); * 2004: Java System.out.printf("%10.2f", x); * 2008: Scala and Groovy printf("%10.2f", x) " The reference and the details (2012): https://news.ycombinator.com/item?id=3964475 https://news.ycombinator.com/item?id=3964475

nwallin 7y ago
In my work life, I have a problem where I have to interface with a stringly typed API. For instance, characters 20-25 in a 400 byte string are a floating point number. No it's not a good API but I don't make decisions. So you need a six character float. "12" is wrong because it's two characters, also "12<four spaces>" is invalid. "1.2e01" is wrong compared to "12.000" because it has (many) more significant digits. ".00001" is wrong compared to "1.2e-5". I don't know how to solve this problem. printf doesn't cut it. It simply can't specify an exact number of characters.
- BeeOnRope 7y ago
  You could try: %06.*g for width 6 down to 1. I believe this will always find an answer, and the one with the largest number of significant digits. For example: void format(double val, int width, char* buf) { for (int w = width; w > 0; w--) { int count = sprintf(buf, "%06.*g", w, val); if (count == width) return; } } "Working" example (unsafe, exits on failure, etc): https://godbolt.org/z/WiaPkT https://godbolt.org/z/WiaPkT Note that you can't represent negative values equal or below -1e-100 since those take 7 characters.

by acqq 7y ago

nwallin 7y ago

In my work life, I have a problem where I have to interface with a stringly typed API. For instance, characters 20-25 in a 400 byte string are a floating point number. No it's not a good API but I don't make decisions. So you need a six character float. "12" is wrong because it's two characters, also "12<four spaces>" is invalid. "1.2e01" is wrong compared to "12.000" because it has (many) more significant digits. ".00001" is wrong compared to "1.2e-5". I don't know how to solve this problem. printf doesn't cut it. It simply can't specify an exact number of characters.

BeeOnRope 7y ago
You could try: %06.*g for width 6 down to 1. I believe this will always find an answer, and the one with the largest number of significant digits. For example: void format(double val, int width, char* buf) { for (int w = width; w > 0; w--) { int count = sprintf(buf, "%06.*g", w, val); if (count == width) return; } } "Working" example (unsafe, exits on failure, etc): https://godbolt.org/z/WiaPkT https://godbolt.org/z/WiaPkT Note that you can't represent negative values equal or below -1e-100 since those take 7 characters.