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printingruststderr

Rust: how to make a formatted print to stderr?

I'm trying to print a formatted string to stderr in Rust (curious newbie here!), but it looks like an easy convenience macro (such as print!/println! for stdout) isn't provided in the standard library.

In C, one could just do it like this:

fprintf(stderr, "format_string", args ...);

I've successfully printed string literals to stderr with 

let stderr = std::io::stderr();
writeln!(&mut stderr, "literal");

The next thing that came into mind was to do a format! first, and then use writeln!, mut that fails to compile with error: expected a literal. On the other hand, stderr.write() expects &[u8], so using String::bytes().collect() doesn't really work either..

What are the correct solutions to this?

Solution

  • See answer of the linked duplicate. Since Rust 1.19, you can use the eprintln! macro.