switched txt to md

qfetchC-notes.txt

@@ -1,213 +0,0 @@
-## The mindset shift: C vs C++
-
-In C:
-
- - ❌ No classes, no RAII, no `std::string`
- - ✅ **You control memory explicitly**
- - ✅ Functions are small, focused, and composable
- - ✅ Portability comes from *conditional compilation*
-
- - “Each function returns ownership of dynamically allocated data, and the caller frees it.”*
-
-## Feature macros (`_POSIX_C_SOURCE`)
-
-```c
-#define _POSIX_C_SOURCE 200809L
-```
-
-### Why this exists
-
-C standard libraries hide some functions unless you *opt in*.
-
-Without it:
-
-* Some systems won’t expose those functions
-* You’ll get mysterious warnings or missing symbols
-
----
-
-## Headers: what C teaches you here
-
-```c
-#include <stdio.h>   // printf, FILE
-#include <stdlib.h>  // malloc, free
-#include <string.h>  // strlen, strdup
-#include <unistd.h>  // POSIX functions
-```
-
-In C:
-
-* Headers are **contracts**
-* If it’s not included, the compiler assumes *nothing*
-
-**Rule of thumb:**
-
-> If you call a function, its header must be included — no exceptions.
-
----
-
-## Conditional compilation (`#if defined(...)`)
-
-Example:
-
-```c
-#if defined(__APPLE__) || defined(__FreeBSD__)
-#include <sys/sysctl.h>
-#endif
-```
-
-### What this teaches you
-
-* C has **no runtime reflection**
-* Portability happens at **compile time**
-* The preprocessor literally removes code before compilation
-
-Think of it as:
-
-```text
-“Only compile this code if the OS supports it.”
-```
-
-This is how *real* portable C software works (git, curl, openssh).
-
----
-
-## The most important function in the file
-
-```c
-static char *dup_or_unknown(const char *s)
-```
-
-### Why this exists
-
-This function enforces a **contract**:
-
-* Every getter:
-
-  * returns a valid `char *`
-  * never returns `NULL`
-  * always returns heap memory
-
-### Why that matters
-
-It lets `main()` be *simple*:
-
-```c
-char *user = get_user();
-/* ... */
-free(user);
-```
-
-No special cases.
-No defensive `if (ptr)` checks.
-
----
-
-## Dynamic allocation patterns (CRITICAL)
-
-Example:
-
-```c
-char *buf = malloc(len);
-snprintf(buf, len, "...", ...);
-return buf;
-```
-
-### This is idiomatic C
-
-Rules being followed:
-
-1. Allocate **exactly what you need**
-2. Initialize before use
-3. Return ownership to the caller
-4. Caller must `free()`
-
-Contrast this with C++:
-
-* No destructors
-* No smart pointers
-* No safety net
-
----
-
-## Why no global buffers?
-
-You *could* have done:
-
-```c
-static char buf[256];
-```
-
-But that would:
-
-* Break thread safety
-* Break reentrancy
-* Make functions non-composable
-
-Dynamic allocation makes your functions:
-
-* Reusable
-* Testable
-* Library-quality
-
----
-
-## Reading system information in C
-
-Each platform teaches a lesson:
-
-### Linux
-
-```c
-/proc/cpuinfo
-/proc/uptime
-```
-
-* Text parsing
-* Line-by-line scanning
-* Defensive string handling
-
-### macOS / BSD
-
-```c
-sysctl()
-```
-
-* Structured kernel APIs
-* Buffer-size negotiation
-* Integer & struct-based data
-
----
-
-## Time handling (classic C pain point)
-
-```c
-time_t now = time(NULL);
-difftime(now, boottime.tv_sec);
-```
-
-Why this matters:
-
-* `time_t` may not be an integer
-* You *never* subtract times directly
-* `difftime()` handles portability
-
----
-
-## The `main()` function: clean by design
-
-```c
-char *user = get_user();
-/* ... */
-free(user);
-```
-
-Notice:
-
-* No logic
-* No parsing
-* No platform checks
-* No error handling clutter
-
-All complexity lives *outside* `main()`.
-