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Errors printing float #669

ofelas opened this Issue Dec 31, 2017 · 2 comments


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ofelas commented Dec 31, 2017

Demonstrated with the following snippet. Tested with version

const warn = @import("std").debug.warn;

// bin/zig version:
// build-exe: a float 3.14
// with --release-safe: a float index out of bounds
//                      Aborted
// with --release-fast: a float Segmentation fault

pub fn main() -> %void {
    var f: f64 = 3.14;
    // the following needs f64() or else error: parameter of type '(float literal)' requires comptime
    // warn("float {}\n", f64(3.14)); // <- uncomment this line and both always work!?!
    warn("a float {.3}\n", f); // same behaviour with and without .3

@andrewrk andrewrk added the bug label Dec 31, 2017

@andrewrk andrewrk added this to the 0.2.0 milestone Dec 31, 2017


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zesterer commented Feb 6, 2018

This problem exists for integer literals as well:

printf("{}", 5);


error: parameter of type '(integer literal)' requires comptime


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tiehuis commented Feb 7, 2018


That isn't the issue presented here. Comptime literals are stored as arbitrary-precision values in the compiler (floats are stored as 128-bit right now). In order to print these, we would have to either bundle compile-time integer support into a runtime or serialize to a string at compile-time which are both fairly untenable as they require a lot of extra machinery/memory that is rather implicit. For this reason we just emit an error (which is a little unhelpful).

I've made a proposal to discuss 'solving' this here: #747.

@andrewrk andrewrk modified the milestones: 0.2.0, 0.3.0 Mar 12, 2018

tiehuis added a commit that referenced this issue Apr 23, 2018

Fix release float printing errors
Fixes #564.
Fixes #669.
Fixes #928.

@andrewrk andrewrk closed this in e5175d4 Apr 29, 2018

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