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Literals 字面量

Definition: In the C programming language, a literal is a fixed, constant value written directly in the source code. Literals represent values that do not change during program execution, and they are used to initialize variables, pass arguments, and express constant data.

C provides several types of literals, each corresponding to a specific data type.

1. Integer Literals

Integer literals represent whole numbers without a fractional part.

Examples:

10 -3 0 255U     // unsigned
123L     // long
0xFF     // hexadecimal
017      // octal
0b1010   // binary (C23 and some compilers)

2. Floating-Point Literals

Floating-point literals represent real numbers with decimals or exponent notation.

Examples:

3.14 -0.5 2.0e3     // exponential notation
4.5f      // float
6.02E-23  // scientific notation

3. Character Literals

Character literals represent single characters enclosed in single quotes.

Examples:

'a' '0' '\n'   // newline escape character
'\x41' // hexadecimal character code (A)

4. String Literals

String literals represent sequences of characters enclosed in double quotes.
They are stored as arrays of char terminated by a null character \0.

Examples:

"Hello" "" "Line1\nLine2"

5. Enumeration Constants

When using enum, each named constant in the enumeration also behaves like an integer literal.

Example:

enum Color { RED = 1, GREEN = 2, BLUE = 3 };

Key Properties of Literals

  • Their values are known at compile time.

  • They have specific types (e.g., int, double, char).

  • They cannot be modified during runtime.

  • String literals have static storage duration and should not be changed.

Example:

const int x = 10;   // 10 is a literal
printf("%s", "Hi"); // "Hi" is a string literal