Dynamic Arrays in C

Post 7 of the Dynamic Arrays in C series · Full source code on GitHub Passing Behavior as Data Our array can store any type, grow on demand, handle errors without corrupting state, and communicate failures through typed error codes. What it cannot do is anything interesting with the elements inside it. We can push, get, set, and insert, operations that treat the elements as opaque byte blobs. We can’t sort the array because sorting requires knowing how to compare two elements. We can’t search it because searching requires knowing what “matching” means. We can’t even destroy it properly when the elements own heap-allocated resources, because the array doesn’t know how to clean them up. ...

Post 6 of the Dynamic Arrays in C series · Full source code on GitHub The Error You’ve Been Ignoring Every function we’ve written so far can fail. array_create calls malloc, twice. array_push calls realloc when the buffer is full. Every one of those calls can return NULL, and every time it does, we’ve printed a message to stderr and returned -1 or NULL. That’s the extent of our error handling: we report the problem and hope the caller notices. ...

Post 5 of the Dynamic Arrays in C series · Full source code on GitHub The Ergonomics Problem Post 4 left us with a working generic array. One struct, one push function, one get function, stores any fixed-size type. The void* engine works. But using it is miserable. To push an integer, you can’t just write array_push(arr, 42). You have to create a variable, then pass its address: int x = 42; array_push(arr, &x);. Two lines for something that should be one expression. To read a value back, you get a void* that you must cast manually: int *val = (int *)array_get(arr, 0);. Every access requires a cast. Every cast is an opportunity to lie to the compiler, write double *val = (double *)array_get(arr, 0) on an int array, and the compiler won’t say a word. You’ll get garbage at runtime and spend an hour wondering why. ...

Post 4 of the Dynamic Arrays in C series · Full source code on GitHub The Limitation We’ve Been Ignoring For three posts, our array has stored integers. Only integers. If you wanted to store floats, you’d write a FloatArray, same struct, same logic, same push function, just with float instead of int everywhere. If you wanted to store a 20-byte struct, you’d write a StructArray. And another for double. And another for char*. Every new type means a new copy of the same code with the same bugs, the same growth logic, the same visualization, the same tests, just with a different type name. ...

Post 3 of the Dynamic Arrays in C series · Full source code on GitHub The Choice We Skipped In Post 2, we solved the “array is full” problem by doubling the capacity on every realloc. We wrote new_cap = old_cap * 2, watched the buffer grow from 2 to 4 to 8 to 16, and moved on. Three reallocations for 12 elementsm, pretty good. But we never justified the number 2. Why not 1.5? Why not 3? Why not just add 100 slots every time? ...

Post 2 of the Dynamic Arrays in C series · Full source code Where We Left Off In Post 1 we built an array that does three things: allocate a fixed buffer, push integers into it, and free everything when we’re done. It works, until it doesn’t. The moment the user pushes one element more than the initial capacity allows, array_push returns -1 and refuses to cooperate. The array is full and there’s nothing we can do about it. ...

Post 1 of the Dynamic Arrays in C series · Full source code The Problem No One Starts With You have five integers. You put them in an array: 1 int numbers[5] = {10, 20, 30, 40, 50}; Done. C gives you a contiguous chunk of 20 bytes on the stack, indexed from 0 to 4, and life is good. Now your user wants to add a sixth integer. What do you do? You can’t resize a stack array. Its size was baked into the binary at compile time, the compiler saw 5, calculated 20 bytes, and that’s the space your function’s stack frame has. There’s no negotiation. You could declare int numbers[1000] and hope it’s big enough, but hope is not a memory management strategy. ...