The original C++ proposal [1] discusses some alternative syntaxes, including underscores. Underscores would conflict with C++ user defined literals, for example

The original C++ proposal [1] discusses some alternative syntaxes, including underscores. Underscores would conflict with C++ user defined literals, for example in 0xAA_BB it is unclear whether _BB is a literal suffix for 0xAA since it’s a valid identifier. [1]: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3499.html https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n34...