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Integer Literal Types in C

• Bare Literals
• Negative Literals
• Literal Suffixes
• Fixed-Width Macros

Bare Literals

Take a look at these variable declarations:

int a = 123;
unsigned int b = 123;
uint64_t c = 123;

We're using the same integer literal, 123, to initialize three different integer types.

In practice, all three initializations work as you'd expect — a, b, and c all end up initialized to the positive integer value one-hundred-and-twenty-three.

But what is the type of the literal 123 taken on its own?

The answer is, it depends.

If a literal is a decimal constant (e.g. 123), its type is the first entry in the following list that can represent its value:

1. int
2. long int
3. long long int

If a literal is an octal or hexadecimal constant (e.g. 0123 or 0x123), its type is the first entry in the following list that can represent its value:

1. int
2. unsigned int
3. long int
4. unsigned long int
5. long long int
6. unsigned long long int

Source: C11 Standard (N1570) 6.4.4.1.

Negative Literals

There are no negative literals.

-123 isn't an integer literal — it's an expression consisting of the positive integer literal 123 and the unary negation operator -.

Literal Suffixes

You can add letter suffixes to specify a literal's type.

u or U makes the type unsigned:

• 123u — unsigned int

l or L makes the type long:

• 123l — long int

ll or LL makes the type long long:

• 123ll — long long int

Combinations work as expected:

• 123ul — unsigned long int
• 123ull — unsigned long long int

Fixed-Width Macros

The stdint.h header contains a set of function macros for adding the appropriate suffixes for fixed-width integer types.

Signed:

• INT8_C()
• INT16_C()
• INT32_C()
• INT64_C()

Unsigned:

• UINT8_C()
• UINT16_C()
• UINT32_C()
• UINT64_C()

For example UINT64_C(123) will expand to 123ULL or 123UL, whichever is appropriate for the system.