There's the following line in C: my_struct->ptr = (char*) data where as you can see, my_struct has a ptr member of type char* I did this on Rust: struct MyStruct { ptr: *mut libc::c_char } then unsafe{*my_struct}.ptr = Box::into_raw(my_data) as *mut libc::c_char where obviously my_struct…

Per the Rust Reference , an unsafe { ... } block is just a variation of a regular block expression { ... }. And further up the same page, it notes: Blocks are always value expressions and evaluate the last operand in value expression context. The distinction between place expressions and value ex…

Where is your *mut MyStruct coming from? Lifetime of MyStruct also needs to be managed somehow, and it may be a dangling pointer (regardless of its content). BTW: #[repr(C)] struct MyStruct { data: Box<MyData>, } is binary-compatible with C struct with a char* field, and you can use that type …

MyStruct is actually mysql's UDF_INIT and it's generated through bindgen so I cannot change it. unsafe{*my_struct}.ptr = Box::into_raw(my_data) as *mut libc::c_char then calling, imediatelly, unsafe{(*my_struct).ptr as *mut MyData}.unwrap() fails Is something wrong on how I set this value?

I suspect this is the summary of what I'm doing: #[derive(Clone, Copy)] struct MyStruct { ptr: *mut libc::c_char } struct MyData{} fn main() { let my_struct = &mut MyStruct{ ptr: std::ptr::null_mut() } as *mut MyStruct; let my_data = Box::new(MyData{}); unsafe{*my_stru…

When you do unsafe{*my_struct}.ptr the unsafe block makes a copy and you assign to the field of that copy. Then when you access the field of the original MyStruct, it never changed. You can see it by removing the Copy implementation. To solve it you can make the unsafe block take the whole line. …

It's a very weird and dangerous way to make a MyStruct pointer. &mut is a temporary loan of a value, and it has to borrow from somewhere. Normally Rust won't let you borrow from an invalid place, but you're using a raw pointer to bypass this protection. In your case the location you're borrowing fr…

the example was just for reducing my problem to a compilation error. On real life, MySQL passes me a pointer to MyStruct, and MySQL itself is responsible for the life of this pointer, so I can do unsafe{*my_struct}.ptr = Box::into_raw(my_data) as *mut libc::c_char; because I've disabled MyData des…

Equivalent of struct->ptr = (char*) data in rust

help

leudz June 11, 2022, 6:36pm 7

I think this thread should answer your question When does dereferencing a pointer create a copy?

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Equivalent of struct->ptr = (char*) data in rust

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