c语言中isdigit函数_在C / C ++中使用isdigit（）

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

翻译自: https://www.journaldev.com/39998/isdigit-in-c-plus-plus

c语言中isdigit函数