My Cargo.toml includes this:
[dependencies]
chrono = "0.4"
And my code includes this:
extern crate chrono;
use chrono::{Duration, DateTime, Utc};
yet when I run my code, I get this error:
error[E0463]: can't find crate for `chrono`
--> src/lib.rs:1:1
|
1 | extern crate chrono;
| ^^^^^^^^^^^^^^^^^^^^ can't find crate
I am working on an Exercism exercise, so the way I am building/running the program is rustc src/lib.rs to test my solution. Is the problem because I'm not running rustc src/main.rs?
When you're directly running rustc, all that compiler knows is the command line arguments. It doesn't know anything about Cargo.toml, in particular, and so it doesn't know where to look for chrono library.
To use dependency management, you have to compile your project with Cargo - just use cargo build/cargo run/cargo test, and everything should be fine. See the Book for details.
If, however, you want (for some reason) use rustc directly, I'd advise to check first cargo anyway, by using cargo build --verbose. It will show all the commands that are invoked, allowing you to inspect the possible arguments to be defined manually.
Related
When creating a project with a test like so:
cargo init --bin projectname
mkdir projectname/tests
echo "extern crate projectname;" > projectname/tests/test.rs
cd projectname/
cargo build
I get this error when testing:
cargo test
Compiling projectname v0.1.0 (file:///home/username/Lab/projectname)
error[E0463]: can't find crate for `projectname`
--> tests/test.rs:1:1
|
1 | extern crate projectname;
| ^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate
How can I access the functions in ´projectname/src/main.rs´ from projectname/tests/test.rs?
How can I access functions in ´projectname/src/main.rs´ from projectname/tests/test.rs?
You cannot.
A binary cannot be used a an external crate (the same way as you can't use a ELF binary as a shared object/library)
You just have to change your initialisation to
cargo init --lib projectname
or rename your main.rs to lib.rs
If you really want to stick with a main, you may look at Rust package with both a library and a binary?.
I start with the cargo new tst. Then in the src/lib.rs I have:
pub struct Config {}
And src/main.rs looks like the following:
use crate::Config;
fn main() {}
This however does not compile:
> cargo run
Compiling tst v0.1.0 (/home/*/rust/book/tst)
error[E0432]: unresolved import `crate::Config`
--> src/main.rs:1:5
|
1 | use crate::Config;
| ^^^^^^^^^^^^^ no `Config` in the root
For more information about this error, try `rustc --explain E0432`.
error: could not compile `tst` due to previous error
But if I replace crate:: with the name of the crate like so:
use tst::Config;
fn main() {}
Then it just work:
> cargo run
Compiling tst v0.1.0 (/home/*/rust/book/tst)
warning: unused import: `tst::Config`
--> src/main.rs:1:5
|
1 | use tst::Config;
| ^^^^^^^^^^^
|
= note: `#[warn(unused_imports)]` on by default
warning: `tst` (bin "tst") generated 1 warning
Finished dev [unoptimized + debuginfo] target(s) in 0.25s
Running `target/debug/tst`
The output for rustc --explain E0432 has the following quote, which if I understand it correctly means, that I can either use the name of a crate or simply crate:::
In Rust 2018, paths in use statements are relative to the current module
unless they begin with the name of a crate or a literal crate::, in which
case they start from the crate root. As in Rust 2015 code, the self:: and
super:: prefixes refer to the current and parent modules respectively.
Am I doing something wrong in here? Is there a way to use code from lib.rs without hardcoding the name of the crate?
> rustc --version
rustc 1.56.1 (Arch Linux rust 1:1.56.1-3)
> cat Cargo.toml
[package]
name = "tst"
version = "0.1.0"
edition = "2021"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[dependencies]
There is no way to refer to “the library crate in my package”; you must refer to it by its name. The Rust compiler doesn't (currently) know anything about other crates that happen to be in the same Cargo package; it just compiles one crate at a time.
In order for this to change, you would need to write a Rust RFC, which would need to include a description of why it would be valuable to have this feature — probably a stronger argument than “it would be less hardcoded”, since main depending on the library is almost certainly going to use library-specific names anyway, so the name of the library itself is a minor issue (unless, I suppose, you're creating many packages from a common template).
I'm trying to work with the rust-http library, and I'd like to use it as the basis for a small project.
I have no idea how to use something that I can't install via rustpkg install <remote_url>. In fact, I found out today that rustpkg is now deprecated.
If I git clone the library and run the appropriate make commands to get it built, how do I use it elsewhere? I.e. how do I actually use extern crate http?
Since Rust 1.0, 99% of all users will use Cargo to manage the dependencies of a project. The TL;DR of the documentation is:
Create a project using cargo new
Edit the generated Cargo.toml file to add dependencies:
[dependencies]
old-http = "0.1.0-pre"
Access the crate in your code:
Rust 2021 and 2018
use old_http::SomeType;
Rust 2015
extern crate old_http;
use old_http::SomeType;
Build the project with cargo build
Cargo will take care of managing the versions, building the dependencies when needed, and passing the correct arguments to the compiler to link together all of the dependencies.
Read The Rust Programming Language for further details on getting started with Cargo. Specifying Dependencies in the Cargo book has details about what kinds of dependencies you can add.
Update
For modern Rust, see this answer.
Original answer
You need to pass the -L flag to rustc to add the directory which contains the compiled http library to the search path. Something like rustc -L path-to-cloned-rust-http-repo/build your-source-file.rs should do.
Tutorial reference
Not related to your post, but it is to your title. Also, cargo based.
Best practice:
external crate named foo
use ::foo;
module (which is part of your code/crate) named foo
use crate::foo;
In both the cases, you can use use foo; instead, but it can lead to confusion.
Once you've built it, you can use the normal extern crate http; in your code. The only trick is that you need to pass the appropriate -L flag to rustc to tell it where to find libhttp.
If you have a submodule in your project in the rust-http directory, and if it builds into its root (I don't actually know where make in rust-http deposits the resulting library), then you can build your own project with rustc -L rust-http pkg.rs. With that -L flag, the extern crate http; line in your pkg.rs will be able to find libhttp in the rust-http subfolder.
I ran into a similar issue. I ended up doing this in my Cargo.toml
[dependencies]
shell = { git = "https://github.com/google/rust-shell" }
Then in my main.rs I was able to add this and compile with success. Note that this cargo package is a macro in my case. Often you will not want to have the #[macro_use] before the extern call.
#[macro_use] extern crate shell;
I am learning rust, now I tried to use Diesel to do some operation to database. I write the main.rs like this:
#[macro_use]
extern crate reddwarf_music;
fn main(){
}
then compile the project using command cargo build, shows error like this:
~/Documents/GitHub/reddwarf_music on develop! ⌚ 14:50:50
$ cargo build ‹ruby-2.7.2›
Compiling reddwarf_music v0.1.0 (/Users/dolphin/Documents/GitHub/reddwarf_music)
error[E0463]: can't find crate for `reddwarf_music`
--> src/main.rs:3:1
|
3 | extern crate reddwarf_music;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate
error: aborting due to previous error
For more information about this error, try `rustc --explain E0463`.
error: could not compile `reddwarf_music`
To learn more, run the command again with --verbose.
(base)
and this is my Cargo.toml:
[package]
name = "reddwarf_music"
version = "0.1.0"
edition = "2018"
[dependencies]
rocket = { version = "0.5.0-rc.1", features = ["json"] }
rand = "0.8.4"
serde = { version = "1.0.64", features = ["derive"] }
serde_json = "1.0.64"
reqwest = "0.11.4"
# database
diesel = { version = "1.4.4", features = ["postgres"] }
dotenv = "0.15.0"
am I doing the right way? the next step I want to use the mod like this:
use reddwarf_music::schema::posts::dsl::*;
I am follow the docs step by step from here to using diesel. what should I do to make it work as expect? the diesel official docs use it like this way. In my project, it did not work.
As far as I can see, the crate you are trying to compile is called reddwarf_music. extern crate tries to include a crate into the crate you're currently compiling. You're in effect trying to include the crate reddwarf_music into itself in order to use proc_macros from reddwarf_music in reddwarf_music. This is unfortunately not possible.
What the official Diesel documentation does is slightly different. Their library crate is called diesel_demo, but the code run when running cargo run --bin is actually the code inside the folder bin, which is not directly a part of the library crate, and instead part of a separate binary crate. If you instead of the file main.rs in the root, create a file inside a bin folder and run cargo build --bin, I think it should work.
(This has been edited to more directly answer the question)
I wrote a program to parse some filenames in Rust using the standard Regex crate. The program runs fine on Linux, but when I tried to compile and run it on Windows, I get some kind of DLL error. I don't really understand what is going on with this, but it's all I have to go on.
This is the compiler version that I'm using:
F:\Coding\rust-shutterstock-deduper\target (master)
λ rustc --version
rustc 1.0.0-nightly (3ef8ff1f8 2015-02-12 00:38:24 +0000)
This is the program that I'm trying to run:
#![feature(plugin)]
#![plugin(regex_macros)]
extern crate regex_macros;
extern crate regex;
fn main() {
let x = regex!(".*");
}
And my Cargo.toml file:
[package]
name = "my_package"
version = "0.0.1"
authors = ["Nate Mara <natemara#gmail.com>"]
[dependencies]
regex = "0.1.14"
regex_macros = "0.1.8"
Are there compiler flags that I should be passing in, or do I need to run this in a special way, or... what am I doing wrong here? I'm just running with cargo run
Add #[no_link] to your code:
#![plugin(regex_macros)]
#[no_link]
extern crate regex_macros;
Right now, plugins are crates, which means they get linked in. The regex_macros crate should tell you to add no_link, but this is a temporary workaround for a Rust issue. However, it looks like this is in the process of being fixed.