How can I print with formatting when debugging a Rust program with GDB?

Question

When I try to print with string formatting, like I do when debugging in C, I get an error of conversion:

(gdb) printf "%s\n", "hello world"
Value can't be converted to integer.

Expected:

(gdb) printf "%s\n", "hello world"
$2 = "hello world"

Diagnostic info:

$ rust-gdb -v
GNU gdb (GDB) 7.12.1
.....

Answer 1

When using printf , it expects the expression to be either a number or a pointer. Pulled from Commands for Controlled Output

printf template, expressions…

The expressions are separated by commas and may be either numbers or pointers

If I had checked the type of "hello world" with gdb's ptype command, I would have noticed that it's an object and not a number or a pointer.

(gdb) ptype "hello world"
type = struct &str {
  data_ptr: u8 *,
  length: usize,
}

To resolve this, change the argument to the string's property called data_ptr .

(gdb) ptype "hello world".data_ptr
type = u8 *

(gdb) p "hello world".data_ptr
$14 = (u8 *) 0x101100080 "hello world\000"

Returning data_ptr should work because it's a pointer ( u8 * ) and it points to an address that is the start of the string.

(gdb) printf "%s\n", "hello world".data_ptr
hello world

---

Be aware not to mix up with print as this wouldn't work .

(gdb) print "%s\n", "hello world".data_ptr
Could not convert character to `UTF-8' character set