> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/man/man9/dnv.9.md).

# dnv.9

`dnvlist_get` — 获取带有默认值的名称/值对的 API

## 名称

`dnvlist_get`, `dnvlist_take`

## 库

libnv

## 概要

```c
#include <sys/dnv.h>

bool
dnvlist_get_bool(const nvlist_t *nvl, const char *name, bool defval);

uint64_t
dnvlist_get_number(const nvlist_t *nvl, const char *name, uint64_t defval);

char *
dnvlist_get_string(const nvlist_t *nvl, const char *name, const char *defval);

nvlist_t *
dnvlist_get_nvlist(const nvlist_t *nvl, const char *name, nvlist_t *defval);

int
dnvlist_get_descriptor(const nvlist_t *nvl, const char *name, int defval);

void *
dnvlist_get_binary(const nvlist_t *nvl, const char *name, size_t *sizep,
    void *defval, size_t defsize);

bool
dnvlist_take_bool(const nvlist_t *nvl, const char *name, bool defval);

uint64_t
dnvlist_take_number(const nvlist_t *nvl, const char *name, uint64_t defval);

char *
dnvlist_take_string(const nvlist_t *nvl, const char *name, const char *defval);

nvlist_t *
dnvlist_take_nvlist(const nvlist_t *nvl, const char *name, nvlist_t *defval);

int
dnvlist_take_descriptor(const nvlist_t *nvl, const char *name, int defval);

void *
dnvlist_take_binary(const nvlist_t *nvl, const char *name, size_t *sizep,
    void *defval, size_t defsize);
```

## 描述

`libnv` 库允许轻松管理名称/值对，并可以通过套接字发送和接收它们。更多信息参见 [nv(9)](/man/man9/nv.9.md)。

`dnvlist_get` 函数返回与 `name` 关联的值。若名为 `name` 的元素不存在，函数返回 `defval` 中提供的值。返回的字符串、nvlist、描述符、二进制数据或数组不得被用户修改，因为它们仍属于该 nvlist。若 nvlist 处于错误状态，尝试使用这些函数中的任何一个都会导致程序中止。

`dnvlist_take` 函数返回与 `name` 关联的值，并从 `nvl` 中移除关联的元素。若名为 `name` 的元素不存在，返回 `defval` 中提供的值。当值为字符串、二进制或数组值时，调用者负责使用 [free(3)](https://github.com/FreeBSD-Ask/freebsd-man-sc/tree/main/man3/free.3.md) 释放返回的内存。当值为 nvlist 时，调用者负责使用 `nvlist_destroy` 销毁返回的 nvlist。当值为描述符时，调用者负责使用 [close(2)](https://github.com/FreeBSD-Ask/freebsd-man-sc/tree/main/man2/close.2.md) 关闭返回的描述符。

## 参见

[close(2)](https://github.com/FreeBSD-Ask/freebsd-man-sc/tree/main/man2/close.2.md), [free(3)](https://github.com/FreeBSD-Ask/freebsd-man-sc/tree/main/man3/free.3.md), [nv(9)](/man/man9/nv.9.md)

## 历史

`dnv` API 出现于 FreeBSD 11.0。

## 作者

`dnv` API 由 Pawel Jakub Dawidek <pawel@dawidek.net> 在 FreeBSD Foundation 赞助下实现。本手册页由 Adam Starak <starak.adam@gmail.com> 编写。


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://book.bsdcn.org/man/man9/dnv.9.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.