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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /compiler/rustc_error_codes/src/error_codes/E0617.md | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'compiler/rustc_error_codes/src/error_codes/E0617.md')
-rw-r--r-- | compiler/rustc_error_codes/src/error_codes/E0617.md | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0617.md b/compiler/rustc_error_codes/src/error_codes/E0617.md new file mode 100644 index 000000000..eed384b49 --- /dev/null +++ b/compiler/rustc_error_codes/src/error_codes/E0617.md @@ -0,0 +1,33 @@ +Attempted to pass an invalid type of variable into a variadic function. + +Erroneous code example: + +```compile_fail,E0617 +# use std::os::raw::{c_char, c_int}; +extern "C" { + fn printf(format: *const c_char, ...) -> c_int; +} + +unsafe { + printf("%f\n\0".as_ptr() as _, 0f32); + // error: cannot pass an `f32` to variadic function, cast to `c_double` +} +``` + +Certain Rust types must be cast before passing them to a variadic function, +because of arcane ABI rules dictated by the C standard. To fix the error, +cast the value to the type specified by the error message (which you may need +to import from `std::os::raw`). + +In this case, `c_double` has the same size as `f64` so we can use it directly: + +```no_run +# use std::os::raw::{c_char, c_int}; +# extern "C" { +# fn printf(format: *const c_char, ...) -> c_int; +# } + +unsafe { + printf("%f\n\0".as_ptr() as _, 0f64); // ok! +} +``` |