c语言中isdigit函数_在C / C ++中使用isdigit（）

野性酷女 2023-02-28 06:28 1阅读 0赞

c语言中isdigit函数

In this article, we’ll take a look at using the isdigit() function in C/C++. This is a very simple way to check if any value is a digit or not. Let’s look at how to use this function, using some simple examples.

在本文中，我们将研究在C / C ++中使用isdigit（）函数。 这是检查任何值是否为数字的非常简单的方法。 让我们通过一些简单的示例来看看如何使用此功能。

--------------------

## C / C ++中isdigit（）的基本语法 **(****Basic Syntax of isdigit() in C/C++****)** ##

This function takes a characer value `val` and returns 0 or 1, if the value is a numerical digit.

此函数采用字符值`val` ，如果该值是数字，则返回0或1。

This is defined in the `<ctypes.h>` header file, so we must also include this file.

这是在`<ctypes.h>`头文件中定义的，因此我们还必须包含此文件。

#include <ctypes.h>
    
    int isdigit(char value);

The value must be of such a form that it can be converted to an `unsigned char`, such as a positive integer / ASCII character.

该值必须具有可以转换为`unsigned char` ，例如正整数/ ASCII字符。

But note that integers will not be considered digits, since only their ascii equivalents are considered.

但请注意，整数将不被视为数字，因为仅考虑其ascii等效项。

### 在C ++中使用isdigit（） **(****Using isdigit() in C++****)** ###

While you can simply copy and paste the C code to C++ too, the C++ standard library already has the implementation of `isdigit()`!

虽然您也可以简单地将C代码复制并粘贴到C ++，但是C ++标准库已经实现了`isdigit()` ！

This make our lives much more simpler, as we can directly use it, from the `std` namespace:

这可以使我们的生活更加简单，因为我们可以从`std`名称空间直接使用它：

std::isdigit(char value);

This also returns a `bool` value instead, but this is equivalent to the integer values 0 and 1, returned by the C version!

它也返回`bool`值，但它等效于C版本返回的整数值0和1！

--------------------

## 在C / C ++中使用isdigit（） **(****Using isdigit() in C/C++****)** ##

Let’s now see some examples to check if a value is a digit or not.

现在，让我们看一些示例来检查值是否为数字。

We’ll take up a few integer numbers and some characters too, and apply `isdigit()` on them.

我们还将使用一些整数和一些字符，并将`isdigit()`应用于它们。

#include <stdio.h>
    #include <ctype.h>
    
    int main() {
        int a = 9;
        int b = 10;
        int c = 49;
        char d = 'a';
        char e = '0';
    
        printf("Is %d a digit?\n", a);
        if (isdigit(a)) printf("Yes\n"); else printf("No\n");
        
        printf("Is %d a digit?\n", b);
        if (isdigit(b)) printf("Yes\n"); else printf("No\n");
        
        printf("Is %d a digit?\n", c);
        if (isdigit(c)) printf("Yes\n"); else printf("No\n");
        
        printf("Is %c a digit?\n", d);
        if (isdigit(d)) printf("Yes\n"); else printf("No\n");
        
        printf("Is %c a digit?\n", e);
        if (isdigit(e)) printf("Yes\n"); else printf("No\n");
        return 0;
    }

**Output**

**输出量**

Is 9 a digit?
    No
    Is 10 a digit?
    No
    Is 49 a digit?
    Yes
    Is a a digit?
    No
    Is 0 a digit?
    Yes

As you can observe, the integers 9 and 10 were not considered digits. But the integer 49 has an ASCII character of ‘0’, and this is a digit!

如您所见，整数9和10不被视为数字。 但是整数49的ASCII字符为“ 0”，这是一个数字！

This is exactly the same as `'0'`, and therefore, this character is also a digit, according to `isdigit(char)`!

这与`'0'`完全相同，因此，根据`isdigit(char)` ，此字符也是一个数字！

--------------------

## 结论 **(****Conclusion****)** ##

In this article, we learned about using the isdigit() function in C/C++. This made us easily check if any character is a digit or not!

在本文中，我们学习了在C / C ++中使用isdigit（）函数的知识。 这使我们可以轻松检查任何字符是否为数字！

You can look at more tutorials on C programming [here][]. Until next time!

您可以在[此处查看][here]有关C编程的更多教程。 直到下一次！

## 参考资料 **(****References****)** ##

*  [Linux manual page][] on isdigit()
    
    isdigit（）上的[Linux手册页][Linux manual page]

--------------------

> 翻译自: [https://www.journaldev.com/39998/isdigit-in-c-plus-plus][https_www.journaldev.com_39998_isdigit-in-c-plus-plus]

c语言中isdigit函数

[here]: https://www.journaldev.com/c-programming
[Linux manual page]: https://linux.die.net/man/3/isdigit
[https_www.journaldev.com_39998_isdigit-in-c-plus-plus]: https://www.journaldev.com/39998/isdigit-in-c-plus-plus