Pretty Printers

Pretty printers allow debuggers to display uint128_t and int128_t values in human-readable format instead of showing the raw struct members. The library contains pretty printers for LLDB, GDB, and Visual Studio in the extra/ folder.

LLDB

To use this, add the following line to your ~/.lldbinit file:

command script import /path/to/int128/extra/int128_printer_lldb.py

If this is successful, you should see the following message in your debugger upon startup:

"int128_t and uint128_t pretty printers loaded successfully"

GDB

To load the pretty printer, add the following line to your .gdbinit:

source /path/to/int128/extra/int128_printer_gdb.py

or you can source it manually in GDB.

(gdb) source /path/to/int128/extra/int128_printer_gdb.py

Visual Studio (NATVIS)

The extra/int128.natvis file provides visualization for the Visual Studio debugger. There are several ways to register it:

Per-Project

Add the .natvis file to your Visual Studio project. In Solution Explorer, right-click the project, select Add > Existing Item, and choose int128.natvis. Visual Studio will automatically use it when debugging that project.

Per-User (All Projects)

Copy int128.natvis to your per-user Visualizers directory:

%USERPROFILE%\Documents\Visual Studio 2022\Visualizers\

Replace 2022 with your Visual Studio version. All projects debugged with that installation will use the visualizer.

CMake Projects

Add the .natvis file as a source file in your CMakeLists.txt:

target_sources(my_target PRIVATE /path/to/int128/extra/int128.natvis)

Display Format

Values that fit in 64 bits are displayed in decimal. Larger values are displayed as a synthesized hexadecimal value with a ' digit separator between the high and low halves.

Type Value Display

Type	Value	Display
`uint128_t`	`42`	`42`
`uint128_t`	`2^64 + 1`	`0x0000000000000001'0000000000000001`
`uint128_t`	`uint128_max`	`0xFFFFFFFFFFFFFFFF’FFFFFFFFFFFFFFFF`
`int128_t`	`42`	`42`
`int128_t`	`-5`	`-5`
`int128_t`	`2^64 + 1`	`0x0000000000000001'0000000000000001`
`int128_t`	`int128_min`	`0x8000000000000000'0000000000000000`

uint128_t

42

uint128_t

2^64 + 1

0x0000000000000001'0000000000000001

uint128_t

uint128_max

0xFFFFFFFFFFFFFFFF’FFFFFFFFFFFFFFFF

int128_t

42

int128_t

-5

int128_t

2^64 + 1

0x0000000000000001'0000000000000001

int128_t

int128_min

0x8000000000000000'0000000000000000

Full decimal display for values beyond 64 bits is not possible in NATVIS. The NATVIS expression evaluator does not support 128-bit arithmetic, so values that exceed the 64-bit range are shown in hexadecimal.

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