How to check release / debug builds using cfg in Rust?
You can use debug_assertions
as the appropriate configuration flag. It works with both #[cfg(...)]
attributes and the cfg!
macro:
#[cfg(debug_assertions)]
fn example() {
println!("Debugging enabled");
}
#[cfg(not(debug_assertions))]
fn example() {
println!("Debugging disabled");
}
fn main() {
if cfg!(debug_assertions) {
println!("Debugging enabled");
} else {
println!("Debugging disabled");
}
#[cfg(debug_assertions)]
println!("Debugging enabled");
#[cfg(not(debug_assertions))]
println!("Debugging disabled");
example();
}
This configuration flag was named as a correct way to do this in this discussion. There is no more suitable built-in condition for now.
From the reference:
debug_assertions
- Enabled by default when compiling without optimizations. This can be used to enable extra debugging code in development but not in production. For example, it controls the behavior of the standard library'sdebug_assert!
macro.
An alternative, slightly more complicated way, is to use #[cfg(feature = "debug")]
and create a build script that enables a "debug" feature for your crate, as shown here.
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ideasman42
Updated on July 31, 2020Comments
-
ideasman42 over 3 years
With the C pre-processor it's common to do,
#if defined(NDEBUG) // release build #endif #if defined(DEBUG) // debug build #endif
Cargo's rough equivalents are:
-
cargo build --release
for release. -
cargo build
for debug.
How would Rust's
#[cfg(...)]
attribute orcfg!(...)
macro be used to do something similar?I understand that Rust's pre-processor doesn't work like C's. I checked the documentation and this page lists some attributes. (assuming this list is comprehensive)
debug_assertions
could be checked, but it may be misleading when used to check for the more general debugging case.I'm not sure if this question should be related to Cargo or not.
-
antoyo over 7 years@Shepmaster This is similar to this question.
-
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turboladen over 4 yearsJust for the record, this doesn't work in build scripts. Just finding this out for myself so thought I'd share.
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BingLi224 about 4 yearsif it's
#[cfg(debug_assertions)]
instead of#[cfg(debug_assertions)] {...}
, there'll beerror[E0658]: attributes on expressions are experimental
anderror: removing an expression is not supported in this position
. Rust 1.42.0