I'm following this blog post on 'comptime' in Zig.
The following line no longer compiles in Zig 0.6.0.
const user_input = try io.readLineSlice(buf[0..]);
Below is the full function:
fn ask_user() !i64 {
var buf: [10]u8 = undefined;
std.debug.warn("A number please: ");
const user_input = try io.readLineSlice(buf[0..]);
return fmt.parseInt(i64, user_input, 10);
}
What is the equivalent in the current version (of getting user input)?
You can use the method readUntilDelimiterOrEof of stdin instead:
const stdin = std.io.getStdIn().reader();
pub fn readUntilDelimiterOrEof(self: #TypeOf(stdin), buf: []u8, delimiter: u8) !?[]u8
So, the code can be:
fn ask_user() !i64 {
const stdin = std.io.getStdIn().reader();
const stdout = std.io.getStdOut().writer();
var buf: [10]u8 = undefined;
try stdout.print("A number please: ", .{});
if (try stdin.readUntilDelimiterOrEof(buf[0..], '\n')) |user_input| {
return std.fmt.parseInt(i64, user_input, 10);
} else {
return #as(i64, 0);
}
}
See also: Zig 0.7.0 documentation.
Related
I've been going through ziglearn and have made my way to ArrayList. I understand the example given there but when I try something a bit more complex I run into errors. Based on the error it seems like my array doesn't have valid memory when it goes to append the new element, but I've set the initial capacity to 10. What am I doing wrong?
const std = #import("std");
const page_allocator = std.heap.page_allocator;
const Allocator = std.mem.Allocator;
const C = struct {
list: std.ArrayList(A),
pub fn init(allocator: Allocator) !*C {
var a = try std.ArrayList(A).initCapacity(allocator, 10);
return &C{ .list = a };
}
pub fn info(self: *C) void {
std.log.info("len {} cap {}", .{ self.list.items.len, self.list.capacity });
}
pub fn addElement(self: *C, a: A) !*C {
try self.list.append(a);
return self;
}
};
const A = struct { e: []const u8 };
test "with arraylist" {
var foo = try C.init(page_allocator);
foo.info();
_ = try foo.addElement(.{ .e = "bar" });
}
Can see below the initial capacity is not 10, it changes with each run pointing to its uninitialized. Am I missing a step to initialize memory for the ArrayList?
[default] (info): len 0 cap 140728248984328
Segmentation fault at address 0x0
/home/john/zig/zig-linux-x86_64-0.10.0/lib/std/mem/Allocator.zig:159:30: 0x219c3c in reallocAdvancedWithRetAddr__anon_4653 (test)
return self.vtable.resize(self.ptr, buf, buf_align, new_len, len_align, ret_addr);
^
/home/john/zig/zig-linux-x86_64-0.10.0/lib/std/mem/Allocator.zig:356:43: 0x216faf in reallocAtLeast__anon_3534 (test)
return self.reallocAdvancedWithRetAddr(old_mem, old_alignment, new_n, .at_least, #returnAddress());
^
/home/john/zig/zig-linux-x86_64-0.10.0/lib/std/array_list.zig:353:89: 0x215697 in ensureTotalCapacityPrecise (test)
const new_memory = try self.allocator.reallocAtLeast(self.allocatedSlice(), new_capacity);
^
/home/john/zig/zig-linux-x86_64-0.10.0/lib/std/array_list.zig:338:55: 0x2170f6 in ensureTotalCapacity (test)
return self.ensureTotalCapacityPrecise(better_capacity);
^
/home/john/zig/zig-linux-x86_64-0.10.0/lib/std/array_list.zig:377:41: 0x21577c in addOne (test)
try self.ensureTotalCapacity(newlen);
^
/home/john/zig/zig-linux-x86_64-0.10.0/lib/std/array_list.zig:167:49: 0x213c16 in append (test)
const new_item_ptr = try self.addOne();
^
src/main.zig:154:29: 0x213b86 in addElement (test)
try self.list.append(a);
^
src/main.zig:165:27: 0x213ce7 in test.with arraylist (test)
_ = try foo.addElement(.{ .e = "bar" });
^
/home/john/zig/zig-linux-x86_64-0.10.0/lib/test_runner.zig:63:28: 0x2164f0 in main (test)
} else test_fn.func();
^
/home/john/zig/zig-linux-x86_64-0.10.0/lib/std/start.zig:596:22: 0x21463b in posixCallMainAndExit (test)
root.main();
^
/home/john/zig/zig-linux-x86_64-0.10.0/lib/std/start.zig:368:5: 0x214101 in _start (test)
#call(.{ .modifier = .never_inline }, posixCallMainAndExit, .{});
^
Your C.init function returns a pointer to C which is on the stack of the init function. This pointer becomes invalid as soon as the function exits.
Just don't return it as a pointer:
pub fn init(allocator: Allocator) !C {
var a = try std.ArrayList(A).initCapacity(allocator, 10);
return C{ .list = a };
}
Or, alternatively, you could put C into the allocator's memory:
pub fn init(allocator: Allocator) !*C {
var result = try allocator.create(C);
result.list = try std.ArrayList(A).initCapacity(allocator, 10);
return result;
}
But avoid doing this unless you have a good reason, as it limits what you can do with C.
Can someone explain me why this piece of code can't be compiled?
const std = #import("std");
const ParseError = error { NotAValidField };
const TestEnum = enum {
field_1,
field_2,
pub fn fromString(str: []const u8) !TestEnum {
switch(true) {
std.mem.eql(u8, "field_1", str) => TestEnum.field_1,
std.mem.eql(u8, "field_2", str) => TestEnum.field_2,
else => ParseError.NotAValidField,
}
}
};
pub fn main() void {
const field = "field_1";
try TestEnum.fromString(field);
}
It results to an error:
./example.zig:11:40: error: unable to evaluate constant expression
std.mem.eql(u8, "field_1", str) => TestEnum.field_1,
Is the compiler trying to figure the str during the compile time while it is passed as an argument? Here's the code in godbolt: https://zig.godbolt.org/z/reK6xv7h5
P.S. I already know there is a std.meta.stringToEnum function.
The compiler sees str in mem.eql call as a runtime value, and thus the error. To specify that str is never used at run time, add a comptime keyword like so:
pub fn fromString(comptime str: []const u8) TestEnum {
return switch (true) {
std.mem.eql(u8, "field_1", str) => TestEnum.field_1,
std.mem.eql(u8, "field_2", str) => TestEnum.field_2,
};
}
Note that all of this comes from wanting to use the mem.eql results to match true. This limits the number of enum values to exactly two and requires the string to be known at compile time. What meta.stringToEnum does instead is to perform the operation at run time.
How can I read a file in zig, and run over it line by line?
I did found os.File.openRead, but it seems old cause it says that container 'std.os' has no member called 'File'.
std.io.reader.readUntilDelimiterOrEof lets your read any std.io.reader line by line. You usually get the reader of something like a file by calling it’s reader() method. So for example:
var file = try std.fs.cwd().openFile("foo.txt", .{});
defer file.close();
var buf_reader = std.io.bufferedReader(file.reader());
var in_stream = buf_reader.reader();
var buf: [1024]u8 = undefined;
while (try in_stream.readUntilDelimiterOrEof(&buf, '\n')) |line| {
// do something with line...
}
The std.io.bufferedReader isn’t mandatory but recommended for better performance.
I muddled through this by looking at the Zig library source/docs, so this might not be the most idiomatic way:
const std = #import("std");
pub fn main() anyerror!void {
// Get an allocator
var gp = std.heap.GeneralPurposeAllocator(.{ .safety = true }){};
defer _ = gp.deinit();
const allocator = &gp.allocator;
// Get the path
var path_buffer: [std.fs.MAX_PATH_BYTES]u8 = undefined;
const path = try std.fs.realpath("./src/main.zig", &path_buffer);
// Open the file
const file = try std.fs.openFileAbsolute(path, .{ .read = true });
defer file.close();
// Read the contents
const buffer_size = 2000;
const file_buffer = try file.readToEndAlloc(allocator, buffer_size);
defer allocator.free(file_buffer);
// Split by "\n" and iterate through the resulting slices of "const []u8"
var iter = std.mem.split(file_buffer, "\n");
var count: usize = 0;
while (iter.next()) |line| : (count += 1) {
std.log.info("{d:>2}: {s}", .{ count, line });
}
}
The above is a little demo program that you should be able to drop into the default project created from zig init-exe, it'll just print out it's own contents, with a line number.
You can also do this without allocators, provided you supply the required buffers.
I'd also recommend checking out this great resource: https://ziglearn.org/chapter-2/#readers-and-writers
Note: I'm currently running a development version of Zig from master (reporting 0.9.0), but I think this has been working for the last few official releases.
To open a file and get a file descriptor back
std.os.open
https://ziglang.org/documentation/0.6.0/std/#std;os.open
To read from the file
std.os.read
https://ziglang.org/documentation/0.6.0/std/#std;os.read
I can't find a .readlines() style function in the zig standard library. You'll have to write your own loop to find the \n characters.
Below is a test case that shows how to create a file, write to it then open the same file and read its content.
const std = #import("std");
const testing = std.testing;
const expect = testing.expect;
test "create a file and then open and read it" {
var tmp_dir = testing.tmpDir(.{}); // This creates a directory under ./zig-cache/tmp/{hash}/test_file
// defer tmp_dir.cleanup(); // commented out this line so, you can see the file after execution finished.
var file1 = try tmp_dir.dir.createFile("test_file", .{ .read = true });
defer file1.close();
const write_buf: []const u8 = "Hello Zig!";
try file1.writeAll(write_buf);
var file2 = try tmp_dir.dir.openFile("test_file", .{});
defer file2.close();
const read_buf = try file2.readToEndAlloc(testing.allocator, 1024);
defer testing.allocator.free(read_buf);
try testing.expect(std.mem.eql(u8, write_buf, read_buf));
}
Check out fs package tests on Github or on your local machine under <zig-install-dir>/lib/fs/test.zig.
Also note that test allocator only works for tests. In your actual source code you need to choose an appropriate allocator.
I am trying to search the binary data of a file in dart, to find the index of a substring. I have working js code but I am unable to convert it to dart. This is the js snippet:
var rp = require('request-promise');
async function test(){
const uri = "https://file-examples-com.github.io/uploads/2017/04/file_example_MP4_480_1_5MG.mp4"
const result = await rp({ uri });
const position = Buffer.from(result).indexOf('dnlu');
console.log(position);
}
test() //outputs 2631582
What would be the dart equivalent of this function?
You'll typically fetch the bytes as a Uint8List.
The Dart Uint8List does not have an indexOf method which works on sublists, so you'll have to search the old fashioned way - by looking at it.
I assume that the bytes represent UTF-8 or Latin-1 characters, and since your string contains only ASCII, you can search for the code units directly.
Maybe you could add something like:
extension IndexOfListExtension<T> on List<T> {
int indexOfAll(List<T> needle, [int start = 0]) {
if (needle.length == 0) return start;
var first = needle[0];
var end = this.length - needle.length;
for (var i = start; i <= end; i++) {
match:
if (this[i] == first) {
for (var j = 1; j < needle.length; j++) {
if (this[i + j] != needle[j]) break match;
}
return i;
}
}
return -1;
}
}
Then you would be able to do:
var bytes = await fetch_the_bytes(uri); // However you want to do this.
var position = bytes.indexOfAll("dnlu".codeUnits);
...
I cannot seem to be able to parse Flow using Babel, its not recognising types or "declare" and is coming up with errors on them :-
const fs = require("fs");
const babel = require("#babel/core");
const parser = require('#babel/parser');
const generate = require('#babel/generator').default;
if (process.argv.length == 3) {
const filename = process.argv[2];
const sourceCode = fs.readFileSync(filename).toString();
console.log("sourceCode = ", sourceCode);
var options = {
"sourceType": "module", // parse in strict mode and allow module declarations
"presets": ["#babel/preset-flow"]
};
const parsedAst = parser.parse(sourceCode, options);
console.log("parsedAst = ", parsedAst)
const { codeOutput, map, ast } = babel.transformFromAstSync(parsedAst, sourceCode, { ast: true } );
console.log("ast = ", JSON.stringify(ast, 2, 2))
const output = generate(ast, { /* options */ }, sourceCode);
console.log("codeOutput = ", codeOutput);
console.log("output = ", output);
};
given the following code :-
// #flow strict
const MAX_SUGGESTIONS = 5;
/**
* Given [ A, B, C ] return ' Did you mean A, B, or C?'.
*/
declare function didYouMean(suggestions: $ReadOnlyArray<string>): string;
// eslint-disable-next-line no-redeclare
declare function didYouMean(
subMessage: string,
suggestions: $ReadOnlyArray<string>,
): string;
// eslint-disable-next-line no-redeclare
export default function didYouMean(firstArg, secondArg?) { ... }
I am getting errors on declare also on types :-
C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:730
throw err;
^
SyntaxError: Unexpected token, expected ";" (8:8)
at Parser._raise (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:723:17)
at Parser.raiseWithData (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:716:17)
at Parser.raise (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:710:17)
at Parser.unexpected (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:8610:16)
at Parser.semicolon (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:8592:40)
at Parser.parseExpressionStatement (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:11449:10)
at Parser.parseStatementContent (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:11050:19)
at Parser.parseStatement (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:10916:17)
at Parser.parseBlockOrModuleBlockBody (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:11490:25)
at Parser.parseBlockBody (C:\Users\aaron\Tests\Babel\generator-test\node_modules\#babel\parser\lib\index.js:11477:10) {
loc: Position { line: 8, column: 8 },
pos: 118
}
Github :-
https://github.com/AaronNGray/babel-flow-parser-test
Tag v0 is without package-lock.json
Need to add some extra details which I cannot think of ???
The following works :-
const fs = require('fs');
const babel = require('#babel/core');
if (process.argv.length == 3) {
const filename = process.argv[2];
const source = fs.readFileSync(filename).toString();
const ast = babel.parseSync(source, {
babelrc: false,
configFile: false,
ast: true,
parserOpts: {
plugins: ['flow', 'jsx'],
},
filename,
});
console.log("ast = ", JSON.stringify(ast, null, 2))
}
I would still like to know if the original will work with modification as its the near enough what is specified in the Babel documentation.