# bson_append_value()

## Synopsis

    #define BSON_APPEND_VALUE(b, key, val) \
       bson_append_value (b, key, (int) strlen (key), (val))

    bool
    bson_append_value (bson_t *bson,
                       const char *key,
                       int key_length,
                       const bson_value_t *value);

## Parameters

- `bson`: A bson_t.

- `key`: An ASCII C string containing the name of the field.

- `key_length`: The length of `key` in bytes, or -1 to determine the length with `strlen()`.

- `value`: A bson_value_t.

## Description

Appends a new field to `bson` by determining the boxed type in `value`. This is useful if you want to copy fields between documents but do not know the field type until runtime.

## Returns

Returns `true` if the operation was applied successfully. The function will fail if appending the value grows `bson` larger than INT32_MAX.