> 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/locale/isdigit.3.md).

# isdigit.3

`isdigit` — 十进制数字字符测试

## 名称

`isdigit`, `isnumber`, `isdigit_l`, `isnumber_l`

## 库

Lb libc

## 概要

`#include <ctype.h>`

`Ft int Fn isdigit int c Ft int Fn isnumber int c Ft int Fn isdigit_l int c locale_t loc Ft int Fn isnumber_l int c locale_t loc`

## 描述

`isdigit` 和 `isdigit_l` 函数测试是否为十进制数字字符。无论 locale 如何，仅包含以下字符：

| `0` | `1` | `2` | `3` | `4` |
| --- | --- | --- | --- | --- |
| `5` | `6` | `7` | `8` | `9` |

`isnumber` 和 `isnumber_l` 函数的行为类似于 `isdigit` 和 `isdigit_l`，但可能识别额外的字符，取决于当前的 locale 设置。

参数的值必须可表示为 `unsigned char` 或 `EOF` 的值。

带 \_l 后缀的版本接受显式的 locale 参数，而不带后缀的版本使用当前的全局或每线程 locale。

## 返回值

`isdigit`、`isdigit_l`、`isnumber` 和 `isnumber_l` 函数在字符测试为假时返回零，在字符测试为真时返回非零。

## 兼容性

在具有大字符集的 locale 中接受超出 `unsigned char` 类型范围的参数的 4.4BSD 扩展被认为过时，可能在未来的版本中不再支持。应改用 `iswdigit` 或 `iswdigit_l` 函数。

## 参见

[ctype(3)](/man/locale/ctype.3.md), [ctype\_l(3)](/man/locale/ctype_l.3.md), iswdigit(3), iswdigit\_l(3), [multibyte(3)](/man/locale/multibyte.3.md), [xlocale(3)](/man/locale/xlocale.3.md), [ascii(7)](/man/man7/ascii.7.md)

## 标准

`isdigit` 函数遵循 ISO/IEC 9899:1990 ("ISO C89")。`isdigit_l` 函数遵循 IEEE Std 1003.1-2008 ("POSIX.1")。

## 历史

`isnumber` 函数出现于 4.4BSD。


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