Problem
Here is the statement of the problem as described by Lawrence Crowl:
- Pronounce
7237498123
- Compare
237498123
with 237499123
for equality - Decide whether
237499123
or 20249472
is larger
The paper then goes on to describe a proposal the C++ standard to add digit separators to C++. In this blog post, we will look at what we can do for this problem in C++ as it currently is.
Doing this involves (ab)using the preprocessor ##
operator which concatenates 2 tokens. Using this yields two different options. We will use the number 1234567
as an example for these 2 options.
Option 1 – Self-contained But Not Terse
1: #define n 1 ## 234 ## 567
2:
3: int j = n;
4:
5: #undef n
This option has the advantage that anyone that knows C would be able to figure out what is going on without looking at any other code. The disadvantage is that this is definitely not terse.
Option 2 – Terse But Requires Macro
Given the macro below:
1: #define NUM_HELPER(a,b,c,d,e,f,g,...) a##b##c##d##e##f##g
2:
3: #define NUM(...) NUM_HELPER(__VA_ARGS__,,,,,,,,,)
we can write the example number 1234567
as below:
1: int j = NUM( 1,234,567 );
The advantage is that this option is terse. It also has the same format that is commonly used outside of programming. The disadvantage is that the code looks pretty confusing unless you know what NUM does. The other disadvantage is that the macro also pollutes the namespace.
While both of these approaches are inferior to C++ native support for digit separators, the two options described above work with C++ now.
Please let me know what you think and which option you like better.
- John Bandela
I started programming in Basic in the 4th grade. In 8th grade, I convinced my parents to buy me Visual C++ 1.0. I discovered I really enjoyed C++, and have been programming in it since. I attended the University of Florida and majored in Computer Science graduating with honors with a 4.0 GPA. I then attending Medical School and obtained my Doctor of Medicine degree.
I have used my computer skills to help me in my medical practice. I also enjoy programming in C++ just for fun, trying to discover new ways of solving problems or applying C++ to new areas. My latest interest has been in creating a component system for C++ allowing components created with 1 compiler to be easily used by another compiler.