rspec/rules/S3543/cfamily/rule.adoc

== Why is this an issue?

{cpp}14 introduced the ability to use a digit separator (``++'++``) to split a literal number into groups of digits for better readability.


To ensure that readability is really improved by using digit separators, this rule verifies:


* *Homogeneity*
**   Except for the left-most group, which can be smaller, all groups in a number should contain the same number of digits. Mixing group sizes is at best confusing for maintainers, and at worst a typographical error that is potentially a bug.

* *Standardization*
**  It is also confusing to regroup digits using a size that is not standard. This rule enforce the following standards:
*** Decimal numbers should be separated using groups of 3 digits.
*** Hexadecimal numbers should be separated using groups of 2 or 4 digits.
*** Octal and Binary should be separated using groups of 2, 3 or 4 digits.

Furthermore, using groups with more than 4 consecutive digits is not allowed because they are difficult for maintainers to read.

=== Noncompliant code example

[source,cpp]
----
long decimal_int_value     = 1'554'3124;          // Noncompliant; mixing groups of 3 and 4 digits
double decimal_float_value = 7'91'87'14.3456;     // Noncompliant; using groups of 2 instead of 3 digits
long hexadecimal_value     = 0x8'3A3'248'6E2;     // Noncompliant; using groups of 3 instead of 2 or 4 digits
long octal_value           = 0442'03433'13726;    // Noncompliant; using groups of 5 instead of 2, 3 or 4 digits.
long binary_value          = 0b01010110'11101010; // Noncompliant; using groups of 8 instead of 2, 3 or 4 digits.
----

=== Compliant solution

[source,cpp]
----
long decimal_int_value     = 15'543'124;
double decimal_float_value = 7'918'714.3456;
long hexadecimal_value     = 0x83'A324'86E2;
long octal_value           = 04'4203'4331'3726;
long binary_value          = 0b0101'0110'1110'1010;
----

include::../exceptions.adoc[]

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== Implementation Specification
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include::../message.adoc[]

include::../highlighting.adoc[]

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== Comments And Links
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include::../comments-and-links.adoc[]

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