C `printf` format cheatsheet

2026-09-30T14:49:54+00:00

1. Standard Integers

The size of these types varies depending on your platform (32-bit vs. 64-bit). Using the correct length modifier prevents data truncation or corruption.

Data Type	Signed Format	Unsigned Format	Safety Notes
`char` (Used as a number)	`%d` or `%i`	`%u`	Automatically promotes to `int` when passed to `printf`.
`short`	`%hd`	`%hu`	The `h` modifier explicitly tells the compiler it is a short integer.
`int`	`%d` or `%i`	`%u`	The default standard integer format.
`long`	`%ld`	`%lu`	The `l` modifier stands for long.
`long long`	`%lld`	`%llu`	The `ll` modifier is used for extra-large integers (guaranteed at least 64 bits).

2. Fixed-Width Integers

When using #include <stdint.h>, these integers have a guaranteed, identical size across all architectures. To print them safely, C uses specific macros available under #include <inttypes.h>:

Data Type	Signed Format	Unsigned Format	printf Syntax Example
`int8_t` / `uint8_t`	`PRId8`	`PRIu8`	`printf("Value: %" PRId8 "\n", var);`
`int16_t` / `uint16_t`	`PRId16`	`PRIu16`	`printf("Value: %" PRIu16 "\n", var);`
`int32_t` / `uint32_t`	`PRId32`	`PRIu32`	`printf("Value: %" PRId32 "\n", var);`
`int64_t` / `uint64_t`	`PRId64`	`PRIu64`	`printf("Value: %" PRIu64 "\n", var);`

3. Floating-Point Numbers

An important rule for printf: float arguments are automatically converted (promoted) into double. Because of this, %f safely works for both types.

Data Type	Standard Format	Scientific Format (e.g., 1.2e+03)	Key Differences
`float`	`%f`	`%e` or `%g`	`%g` automatically selects the shortest representation.
`double`	`%f` (or `%lf`)	`%e` or `%g`	While `%f` works for printf, the input function scanf strictly requires `%lf` for a double.
`long double`	`%Lf`	`%Le` or `%Lg`	Must use a capital `L` modifier.

4. Characters, Strings, and Pointers

Handling text and memory addresses poses security risks if incorrect formatting is used.

Data Type	Safe Format	Safety Notes
`char` (Character)	`%c`	Prints a single ASCII character.
`char*` or `char[]` (String)	`%s`	The string must end with a null character (`\0`). If missing, `printf` will read past bounds and crash.
Any Pointer Type (Address)	`%p`	Prints memory addresses in hexadecimal. Explicitly cast the argument to `(void*)` for full compliance.

5. Memory Management & System Adaptive Types (C99+)

These specifiers ensure your code compiles and prints safely on both 32-bit and 64-bit systems without manual architecture adjustments:

Data Type	Safe Format	Real-World Use Case
`size_t`	`%zu`	Used for physical object sizes, array capacities, or `sizeof` operator returns.
`ssize_t`	`%zd`	A signed version of `size_t` (commonly returned by file system operations like `read()` or `write()`).
`ptrdiff_t`	`%td`	Represents the distance or index difference between two pointers in the same array.

💡 General Safety Rules

String Protection: If a string might lack a \0 terminator, cap the maximum printed width using %.10s (prints up to 10 characters only).
Literal Percent: To display an actual % symbol on the screen, escape it by doubling it up: %%.