ziglings/exercises/096_memory_allocation.zig

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//
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// In most of the examples so far, the inputs are known at compile
// time, thus the amount of memory used by the program is fixed.
// However, if responding to input whose size is not known at compile
// time, such as:
// - user input via command-line arguments
// - inputs from another program
//
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// You'll need to request memory for your program to be allocated by
// your operating system at runtime.
//
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// Zig provides several different allocators. In the Zig
// documentation, it recommends the Arena allocator for simple
// programs which allocate once and then exit:
//
// const std = @import("std");
//
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// // memory allocation can fail, so the return type is !void
// pub fn main() !void {
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//
// var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
// defer arena.deinit();
//
// const allocator = arena.allocator();
//
// const ptr = try allocator.create(i32);
// std.debug.print("ptr={*}\n", .{ptr});
//
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// const slice_ptr = try allocator.alloc(f64, 5);
// std.debug.print("slice_ptr={*}\n", .{slice_ptr});
// }
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// Instead of an simple integer or a constant sized slice, this
// program requires a slice to be allocated that is the same size as
// an input array.
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// Given a series of numbers, take the running average. In other
// words, each item N should contain the average of the last N
// elements.
const std = @import("std");
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fn runningAverage(arr: []const f64, avg: []f64) void {
var sum: f64 = 0;
for (0.., arr) |index, val| {
sum += val;
const f_index: f64 = @floatFromInt(index + 1);
avg[index] = sum / f_index;
}
}
pub fn main() !void {
// pretend this was defined by reading in user input
var arr: []const f64 = &[_]f64{ 0.3, 0.2, 0.1, 0.1, 0.4 };
// initialize the allocator
var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
// free the memory on exit
defer arena.deinit();
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// initialize the allocator
const allocator = arena.allocator();
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// allocate memory for this array
var avg: []f64 = ???;
runningAverage(arr, avg);
std.debug.print("Running Average: ", .{});
for (avg) |val| {
std.debug.print("{d:.2} ", .{val});
}
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std.debug.print("\n", .{});
}
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// For more details on memory allocation and the different types of
// memory allocators, see https://www.youtube.com/watch?v=vHWiDx_l4V0