测试转换为int的int字符是否为数字c ++

Question

I would like to know how to test if a char is a number. An int has been converted to char and later on I want to see if this char is a number.

int num = 2;
char number = '2';
char num2 = (char)num;
cout << "Non comverted: " << number << " " << num2 << endl;
cout << "comverted: " << static_cast<int>(number) << " " << static_cast<int>(num2) << endl;
if (isdigit(number))
  cout << "number" << endl;
else if (isdigit(num2))
  cout << "num2" << endl;
else cout << "none" << endl;

when I run this the second if should also be able to relate to true.

The reason why I want to be able to do this is because I store a lot of different values into a char array and would later like to know when something is a number or not.

Thanx a lot

Answer 1

要将整数从int转换为ascii / utf8字符，有一个非常简单的转换：

char num2 = static_cast<char>('0' + num);

Answer 2

This:

char num2 = (char)num;

Does not make sense. You're casting a 2 to a char which will give you ASCII code for STX, a special character ( http://www.asciitable.com/ ).

You probably want this:

char num2 = '0' + num;

What that does is give you a character counted from ASCII '0', so it will work up to 9, after which you will get other characters as seen in the ASCII table.

Answer 3

You aren't actually converting num to a number. Your line 3 basically results in:

char num2 = (char)2;

The ASCII character with decimal value 2 is not a digit. In fact, it is not printable. The easiest way to convert a single digit integer to its printable char is to add '0' to it:

char num2 = '0' + num;

The reason for this is that the character 0 is the first digit in the ASCII table , directly followed by 1, 2, 3, etc...

Edit

As Christian Hackl points out in the comments, c++ does not require an implementation to use ASCII , although it is guaranteed that the digits 0 through 9 are represented by contiguous integer values.