PSA: A new compiler has entered the game

Okay not really, it’s the lecturer’s wrapper for clang, which has pretty love messages (error messages in red) when things go wrong.

Compiling a single file

2521 3c -o prog prog.c

Compiling from multiple files

2521 3c -o prog prog.c f2.c f3.c

Compiling with leak checking

2521 3c +leak -o prog prog.c f2.c f3.c

Switch Statements

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switch (variable) {
  case a:
    ...
    break;
  case b:
    ...
    break;
  case c:
    ...
    break;
}

Equivalent to

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if (variable == a) {
  ...
} else if (variable == b) {
  ...
} else if (variable == c) {

}

The default case

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switch() {
  case: ...
  case: ...
  default:
    ...
}

Misc

• Function prototypes don’t need a variable name, only the type

break, continue, return

• break - exit a loop
• continue - steps through the loop to the next iteration
• return - exit a function (exits a loop implicitly)

function pointers

return_t (*var)(arg_t, …)

int -> int: int (*fp)(int);
(int, int) -> void: void(*fp2)(int,int);

When malloc‘ing structs

If we’re using a pointer type, remember to pass in the actual struct to malloc

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struct st;
typedef struct st *St;

/* 1 */ St st_ptr = malloc(sizeof(St));      // Will ONLY malloc 4 bytes (sizeof a pointer)
/* 2 */ St st_ptr = malloc(sizeof(*st_ptr)); // Would malloc the space we need

• Can’t dereference a typedef’d struct
• #2 - sizeof(*st_ptr) -> dereferencing during declaration to give us struct st

And a summary of a summary of gdb