C

This is part two of two. Part one covers variables, symbolic constants, and the preprocessor. C always evaluates expressions before executing C evaluates every expression before running it. If main is missing, the linker signals an error, that’s the entry point contract. Parameters to main (argc, argv) behave like local variables. No garbage collector In C there’s no garbage collector. Local variables are not “objects” managed by a runtime; they’re temporary allocations on registers or the stack. When the function returns, they’re gone. There’s no tracing, no finalization, no safety net. This is by design. ...

This is part one of two. Part two covers the C memory model and stack frames. -Wall If I use the -Wall flag, the compiler emits warnings. Simple rule: always use it. 0 means more than zero The value 0 is equivalent to false in C boolean expressions. It also shows up in shell short-circuit evaluation. In an expression like ./a.out && ls, ls only executes if ./a.out returns 0. That’s because 0 is the success exit code, and && short-circuits on failure. So ./a.out returning 0 makes ls run. The 0 in the exit code sense is “success / true” from the shell’s perspective, opposite of the C boolean convention, which trips people up. ...

In the previous post, we saw that dynamically linked binaries don’t include library code, they just reference it. Which raises an obvious question: who actually loads that code at runtime, and how does the program find it? The answer is ld.so, the dynamic linker. And it runs before your main() does. The Bootstrap Problem When you execute a binary, the kernel reads its ELF header. One of the fields in that header (stored in the .interp section) contains a path like: ...

Most developers treat compilation as a black box: you put source code in, you get a binary out. But there are actually three distinct stages happening, each with its own job and its own output. Understanding them has made me significantly better at debugging linker errors, understanding dependencies, and reasoning about what ends up in a binary. Let’s walk through what happens when you run gcc hello.c -o hello. Stage 1: The Preprocessor Before the compiler sees a single line of your code, the preprocessor runs. Its job is mechanical: it handles all the # directives. ...