[THRIFT-5496] Thrift compiler (C/C++) truncates small doubles to a fixed number of digits after the decimal point

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 0.15.0
• Component/s: C++ - Compiler
• Assignee: Unassigned
• Reporter: Richard H. Gumpertz
• Created: 09/Jan/22 21:22
• Updated: 20/Oct/23 09:45

Description

When the Thrift C++ compiler generates double constants in .h files, it
    (1) doesn't use scientific notation (e.g., 123.45e-22)
    (2) uses a fixed number of digits after the decimal point

Hence, if the constant to be generated is small but non-zero, it shows up as "0.0000000000000000" (17 digits of precision, 16 after the decimal point).

(1) Would somebody please explain why scientific notation is not used when appropriate?

(2) Assuming that there is a good reason for not using scientific notation, I have created a fix that instead generates "0.000000000000000000012345000000000000" (17 digits of precision following the 19 '0's between the decimal point and the '1'. 

I made this fix in .../generate/t_erl_generator.cc,, .../generate/t_generator.cc,, and .../test/DoubleConstantsTest.thrift. 

I will submit a github pull request shortly.

Issue Links

• links to: GitHub Pull Request #2502