How to safely get string literal from String

[candid lagoon]

I want to format a string loaded in from a file

error: format argument must be a string literal
--> src/main.rs:22:31
|
22 | let config_html = format!(config_html_skeleton, String::from("data:application/octet-stream;charset=utf-8;base64,") + &encod...
| ^^^^^^^^^^^^^^^^^^^^
|
help: you might be missing a string literal to format with
|
22 | let config_html = format!("{} {}", config_html_skeleton, String::from("data:application/octet-stream;charset=utf-8;base64,") + &encode(configfile));
| ++++++++

error: argument must be a string literal
--> src/main.rs:23:27
|
23 | println!(include_str!(config_html_skeleton));
| ^^^^^^^^

let config_html_skeleton = include_str!("../config-button.html");
let config_html = format!(config_html_skeleton, String::from("data:application/octet-stream;charset=utf-8;base64,") + &encode(configfile));
println!(include_str!(config_html_skeleton));

[limber egret]

Maybe include_str!() help

Or custom proc_macro

There is no way to get a literal at runtime from file, just because literal is part of syntax, not a value category

Also, iirc, there is a format method present in stdlib, which does the same, but without static verification

[candid lagoon]

gotcha Ill have a look for that

[steep coral]

Also for your println thing, you just need to put it in the args:

println!("{}", config_html_skeleton);

[candid lagoon]

when I try that it ends up wanting more if that makes sense?
ill post error

neverming misread my error from before

[limber egret]

Ah, sorry, you tried include_str, I didn't see at first time

[willow aurora]

why not println!("{}",include_str!(config_html_skeleton)); ?

[steep coral]

You can't include_str runtime values

[candid lagoon]

hmm so if i pass include_str in arguments it stays on the stack and I dont need to worry about memory leaks?

[steep coral]

Nothing about this concerns the stack or memory leaks.

[candid lagoon]

gotcha

[limber egret]

https://doc.rust-lang.org/std/fmt/fn.format.html

[verbal mist]

That requires having an Arguments, which can only be made by format_args!, which still requires a string literal as the format string

[limber egret]

Hm, looks like that will not work... Its only to back format!()...

[verbal mist]

Also: if you put include_str! directly in the println!/format! invocation, it will work

[candid lagoon]

this worked

[steep coral]

no it didn't

[candid lagoon]

but its printing on my console

[verbal mist]

$ cat a.rs
fn main() {
    println!(include_str!("hello.txt"), "world");
}
$ cat hello.txt 
Hello, {}!
$ rustc a.rs && ./a
Hello, world!

[verbal mist]

It will work, but it won't do any interpolation of any {}s in config_html_skeleton

[candid lagoon]

let config_html = format!(include_str!("../config-button.html"), String::from("data:application/octet-stream;charset=utf-8;base64,") + &encode(configfile));
println!("{}", config_html);

[steep coral]

No what, you can't pass anything except a string literal to include_str.

[limber egret]

You just use include_str improperly. it doesn't transform variable to literal - it just loads file contents at compile time

[steep coral]

This looks fine, but it can be improved by using format_args to avoid creating the temporary string

let config_html = format!(
  include_str!("../config-button.html"),
  format_args!(
    "data:application/octet-stream;charset=utf-8;base64,{}",
    &encode(configfile)
  )
);
println!("{}", config_html);

[verbal mist]

Oh, I misread it as println!("{}",include_str!("config_html_skeleton"));

[steep coral]

Normally this wouldn't matter much, but you're copying an entire base64-encoded thing so I'm mentioning it.