Linux-Kernel-Internals

- Linux Kernel Internals: https://ankitkdev.com/blog/
- Char Driver: https://ankitkdev.com/blog/linux-kernel/device-driver/char-driver/
- fasync Method: https://ankitkdev.com/blog/linux-kernel/device-driver/fasync/
- Ioctl Interface: https://ankitkdev.com/blog/linux-kernel/device-driver/ioctl/
- Poll Method: https://ankitkdev.com/blog/linux-kernel/device-driver/poll/
- Proc-Interface: https://ankitkdev.com/blog/linux-kernel/device-driver/proc/
- Completion-Variable: https://ankitkdev.com/blog/linux-kernel/deferred-work/completion-variable/
- Tasklet: https://ankitkdev.com/blog/linux-kernel/deferred-work/tasklet/
- Timers: https://ankitkdev.com/blog/linux-kernel/deferred-work/timer/
- Wait Queue: https://ankitkdev.com/blog/linux-kernel/deferred-work/wait-queue/
- container_of(): https://ankitkdev.com/blog/linux-kernel/macros/container_of/
- Debugging Macros: https://ankitkdev.com/blog/linux-kernel/macros/debug/
- Module Parameters: https://ankitkdev.com/blog/linux-kernel/macros/kernel-module/
- pr_fmt(): https://ankitkdev.com/blog/linux-kernel/macros/pr-family/
- Stringification: https://ankitkdev.com/blog/linux-kernel/macros/string/
- Error Handling with Pointers: https://ankitkdev.com/blog/kernal-internals/error-handling/
- Kbuild Makefile: https://ankitkdev.com/blog/kernal-internals/kbuild/
- SLUB debug: https://ankitkdev.com/blog/kernel-debugging/debug-slub-memory/
- C Memory Layout: https://ankitkdev.com/blog/c/c-memory-layout/
- do { ... } while (0): https://ankitkdev.com/blog/c/do-while-loop/
- Error Handling: https://ankitkdev.com/blog/c/error-handling/
- Forward Declarations: https://ankitkdev.com/blog/c/forward-declaration-in-c/
- Return value by Macro: https://ankitkdev.com/blog/c/return-by-macro/
- unsigned :\ 0 Bit-Fields in c: https://ankitkdev.com/blog/c/zero-width-bit-field/
- Variadic Macro: https://ankitkdev.com/blog/c/variadic-macro/
- Zero Padding in C: https://ankitkdev.com/blog/c/padding/
- programming concepts: https://ankitkdev.com/blog/theory/
- Build & Install Linux Kernel for BBB: https://ankitkdev.com/blog/misc/build-linux-kernel-BBB/
- Configure U-boot for BBB: https://ankitkdev.com/blog/misc/configure-uboot-bbb/
- Install Ubuntu Server on Qemu: https://ankitkdev.com/blog/misc/install-ubuntu-server-on-qemu/
- Linux Kernel Mentorship Program: https://ankitkdev.com/blog/misc/linux-kernel-mentorship-program/
- Reverse-Engineer apk/apks files: https://ankitkdev.com/blog/misc/debug-apk/


# Zero Padding in C with `printf`

In C, `printf()` can add leading zeros to make a number occupy a fixed minimum width.

The syntax is:

```c 
%0<width><specifier>
```

For example:

```c
printf("%06d", 123);
```


Output:

```text
000123
```

Here:

* `0` → pad with zeros
* `6` → minimum field width is 6 characters
* `d` → print a signed decimal integer

### Zero padding vs space padding

```c
printf("%06d", 123);
```

Output:

```text
000123
```

while:

```c
printf("%6d", 123);
```

Output:

```text
   123
```

So:

```text
%06d → zero padding
%6d  → space padding
```

### Example: hexadecimal

```c
printf("0x%08lx\n", value);
```

For:

```c
value = 0x1234;
```

the output is:

```text
0x00001234
```

`%08lx` means:

* `0` → zero padding
* `8` → minimum width of 8 characters
* `l` → `long`
* `x` → hexadecimal

Zero padding is useful when displaying **IDs, hexadecimal values, timestamps, counters, or other fixed-width numbers** where aligned output is desirable.