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#020
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Resource management is hard in C. You have to remember to free memory, close files, and release locks. If you return early from a function, it’s easy to forget a cleanup step. Zig solves this with defer.
How Defer Works
The defer statement schedules a block of code to run when the current scope exits. It doesn’t matter how the scope exits—whether by return, reaching the end, or breaking from a loop.
fn processFile() !void { var file = try std.fs.cwd().openFile("data.txt", .{}); // This will run when the function returns, no matter what defer file.close();
var buffer: [1024]u8 = undefined; const bytes_read = try file.readAll(&buffer); // ... process data ...}Memory Management
defer is especially useful with allocators. You can allocate memory and immediately schedule its release.
fn heavyComputation(allocator: std.mem.Allocator) !void { const data = try allocator.alloc(u8, 1024); defer allocator.free(data);
// Use 'data' safely knowing it will be freed // even if an error occurs later try performStep1(data); try performStep2(data);}Stack-Like Execution
If you have multiple defer statements, they run in reverse order of definition (LIFO).
{ defer std.debug.print("First\n", .{}); defer std.debug.print("Second\n", .{}); // Prints: // Second // First}This simple keyword eliminates a whole class of resource leak bugs.
