C++ Primer（English Version）Page40 Table 2.2 是需要记忆一下的。（有些记不住，就记了下笔记）
Character and Character String Literals
| Prefix | Meaning / Type |
|---|---|
| u | Unicode 16 character / char16_t |
| U | Unicode 32 character / char32_t |
| L | wide character / wchar_t |
| u8 | utf-8 (string literals only) / char |
Integer Literals
| Suffix | Minimum Type |
|---|---|
| u or U | unsigned |
| l or L | long |
| ll or LL | long long |
Floating-Point Literals
| Suffix | Type |
|---|---|
| f or F | float |
| l or L | long double |
示例请见【C++ Primer(5th Edition) Exercise】练习程序 - Chapter2（第二章）Exercise 2.5 & 2.7。