---
name: "mongoc_debugging"
section: "3"
platform: "linux"
package: "libmongoc-doc"
version: "1.23.1-1+deb12u3"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/mongoc_debugging"
---

# mongoc\_debugging(3)

Aids for Debugging

## NAME

mongoc\_debugging - Aids for Debugging

## GDB

This repository contains a **.gdbinit** file that contains helper functions to aid debugging of data structures. GDB will load this file *automatically* if you have added the directory which contains the *.gdbinit* file to GDB's *auto-load safe-path*, *and* you start GDB from the directory which holds the *.gdbinit* file.

You can see the safe-path with **show auto-load safe-path** on a GDB prompt. You can configure it by setting it in **~/.gdbinit** with:

```
add-auto-load-safe-path /path/to/mongo-c-driver
```

If you haven't added the path to your auto-load safe-path, or start GDB in another directory, load the file with:

```
source path/to/mongo-c-driver/.gdbinit
```

The **.gdbinit** file defines the **printbson** function, which shows the contents of a **bson\_t \*** variable. If you have a local **bson\_t**, then you must prefix the variable with a *&*.

An example GDB session looks like:

```
(gdb) printbson bson
ALLOC [0x555556cd7310 + 0] (len=475)
{
    'bool' : true,
    'int32' : NumberInt("42"),
    'int64' : NumberLong("3000000042"),
    'string' : "Stŕìñg",
    'objectId' : ObjectID("5A1442F3122D331C3C6757E1"),
    'utcDateTime' : UTCDateTime(1511277299031),
    'arrayOfInts' : [
        '0' : NumberInt("1"),
        '1' : NumberInt("2")
    ],
    'embeddedDocument' : {
        'arrayOfStrings' : [
            '0' : "one",
            '1' : "two"
        ],
        'double' : 2.718280,
        'notherDoc' : {
            'true' : NumberInt("1"),
            'false' : false
        }
    },
    'binary' : Binary("02", "3031343532333637"),
    'regex' : Regex("@[a-z]+@", "im"),
    'null' : null,
    'js' : JavaScript("print foo"),
    'jsws' : JavaScript("print foo") with scope: {
        'f' : NumberInt("42"),
        'a' : [
            '0' : 3.141593,
            '1' : 2.718282
        ]
    },
    'timestamp' : Timestamp(4294967295, 4294967295),
    'double' : 3.141593
}
```

## LLDB

This repository also includes a script that customizes LLDB's standard **print** command to print a **bson\_t** or **bson\_t \*** as JSON:

```
(lldb) print b
(bson_t) $0 = {"x": 1, "y": 2}
```

The custom **bson** command provides more options:

```
(lldb) bson --verbose b
len=19
flags=INLINE|STATIC
{
  "x": 1,
  "y": 2
}
(lldb) bson --raw b
'\x13\x00\x00\x00\x10x\x00\x01\x00\x00\x00\x10y\x00\x02\x00\x00\x00\x00'
```

Type **help bson** for a list of options.

The script requires a build of libbson with debug symbols, and an installation of *PyMongo*. Install PyMongo with:

```
python -m pip install pymongo
```

If you see "No module named pip" then you must *install pip*, then run the previous command again.

Create a file **~/.lldbinit** containing:

```
command script import /path/to/mongo-c-driver/lldb_bson.py
```

If you see "bson command installed by lldb\_bson" at the beginning of your LLDB session, you've installed the script correctly.

## DEBUG ASSERTIONS

To enable runtime debug assertions, configure with **-DENABLE\_DEBUG\_ASSERTIONS=ON**.

## AUTHOR

MongoDB, Inc

## COPYRIGHT

2017-present, MongoDB, Inc