如何在 GDB 中漂亮地打印 Rust HashMap？

Question

Here is a simple Rust example with a Vec and HashMap that I am running in GDB:

use std::collections::HashMap;

fn main() {
    let v = vec!["Mon", "Tue", "Wed"];
    println!("{:?}", v);

    let mut h = HashMap::new();
    h.insert(1,"Jan");
    h.insert(2,"Feb");
    h.insert(3,"Mar");
    h.insert(4,"Apr");
    println!("{:?}", h);
}

When I view the Vec it is pretty-printed, while the HashMap isn't:

bash$ rust-gdb target/debug/test_hashmap
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Reading symbols from target/debug/test_hashmap...done.
(gdb) b 12
Breakpoint 1 at 0xa056: file src/main.rs, line 12.
(gdb) r
Starting program: /home/john/proj/test_hashmap/target/debug/test_hashmap 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
["Mon", "Tue", "Wed"]

Breakpoint 1, test_hashmap::main () at src/main.rs:12
12          println!("{:?}", h);
(gdb) p v
$1 = Vec<&str>(len: 3, cap: 3) = {"Mon", "Tue", "Wed"}
(gdb) p h
$2 = HashMap<i32, &str, std::collections::hash::map::RandomState> = {hash_builder = RandomState = {k0 = 12919411587537124140, 
    k1 = 836420561220520453}, table = RawTable<i32, &str> = {capacity_mask = 31, size = 4, hashes = TaggedHashUintPtr = {
      Unique<usize> = {pointer = NonZero<*const usize> = {0x7ffff6c1c400}, _marker = PhantomData<usize>}}, 
    marker = PhantomData<(i32, &str)>}, resize_policy = DefaultResizePolicy}
(gdb) info pretty-printer
global pretty-printers:
  builtin
    mpx_bound128
  objfile /home/john/proj/test_hashmap/target/debug/test_hashmap pretty-printers:
  rust_pretty_printer_lookup_function
(gdb) n
{1: "Jan", 4: "Apr", 3: "Mar", 2: "Feb"}
13      }
(gdb) 

The program sees the HashMap (and prints its values ok), but I can't see those inside GDB. The Rust pretty printer seems to be enabled because Vec is printed out just fine.

How can I get the HashMap keys and values in regular GDB?

Answer 1

At the moment it is not possible to pretty-print key-values items for an HashMap .

There is an open issue requesting this feature .

Answer 2

Pretty printing a BTreeMap will be enabled if this PR is merged .

Both BTreeMap and HashMap APIs are similar. So, you may be able to replace HashMap and BTreeMap for debugging.

Answer 3

您可以使用 rust-gdb/rust-lldb，它可以漂亮地打印 HashMap 的键值项。