CODEWITHSUNDEEP
rustlifetimeborrow-checkerborrow
saga
saga

Reputation: 2113

Converting a Vec<&str> to Vec<&CStr> in rust

Take a look at this function:

fn exec(cli: Vec<&str>) {
    eprintln!("execing: {:?}", cli);
    let args: Vec<&CStr> = cli.iter()
        .map(|s| CString::new(s.as_bytes()).unwrap().as_c_str())
        .collect();
    execv(args[0], &args);
    debug(args);
}

It takes a Vec<&str> and executes it as a command. I'm having trouble converting this to Vec<&CStr> (which is what execv needs). Compiler reports this error for the map operations:

error[E0515]: cannot return value referencing temporary value
   --> src/idea.rs:141:18
    |
141 |         .map(|s| CString::new(s.as_bytes()).unwrap().as_c_str())
    |                  -----------------------------------^^^^^^^^^^^
    |                  |
    |                  returns a value referencing data owned by the current function
    |                  temporary value created here

How do I fix this error?

Upvotes: 2

Views: 447

Answers (1)

MaxV
MaxV

Reputation: 2810

You have to collect all CString to a separated vector so you references will be valid during execv call:

use std::ffi::CString;
use std::ffi::CStr;

fn main() {
    let cli = vec!["hello", "world"];
    let vec: Vec<_> = cli.iter()
        .map(|s| CString::new(s.as_bytes()).unwrap())
        .collect();
    let vec_obj: Vec<&CStr> = vec.iter().map(|c| c.as_c_str()).collect();
    println!("CString:{:?}", vec);
    println!("&CStr:{:?}", vec_obj);
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=c440ea898abe2ed5573993923ee6b74f

Upvotes: 2

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