C Proposal - Allow underscores in numbers

C-Number-underscore.md

Document number	Nnnnn=yy-nnnn
Date:	yyyy-mm-dd
Project	Programming Language C++, Library Working Group
Reply-to	this document

I. Table of Contents

• This
• Introduction
• Motivation and Scope
• Impact
• Design Decisions
• Technical Specifications
• Acknowledgements
• References

II. Introduction

• Allow _ in numbers as non-breaking-zero-width-space (or otherwise ignored when gathering a number) 1_123.000_000_001 allowing them anywhere after a number token starts (0-9, -(?), +(?)). The _ are not retained as part of the number, and no printing will restore them other than custom user routines. Nearly all other languages now support this.
• ECMA SCRIPT proposal Has references to other languages' implementation.

III. Motivation and Scope

• Adds convenience feature for coding numbers. 0x33_45_33_42 for example.

IV. Impact On the Standard

• All valid code previously written still behaves the same way.

V. Design Decisions

• See ECMA Proprosal for more information.

VI. Technical Specifications

• None Provided

VII. Acknowledgements

• None known, no previous proposals have been mentioned.

VIII. References

• ECMA Script Proposal
• 'In case anyone is curious, the original digit separators proposal did use underscores: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2281.html
  • A subsequent draft included a whole bunch of different options: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3499.html
  • Before going back to underscore: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3661.html
  • and finally the single quote we've had since C++14: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3781.pdf'

Allow underscore in numbers for formatting

Allow _ in numbers as non-breaking-zero-width-space (or otherwise ignored when gathering a number) 1_123.000_000_001 allowing them anywhere after a number token starts (0-9, -(?), +(?)). The _ are not retained as part of the number, and no printing will restore them other than custom user routines.

Nearly all other languages now support this.