Should `isdigit()` Take a `char` or `int` Input?

Is isdigit() Function Intended for Char or Int Input?

In the provided code snippet, the if condition employs isdigit() to determine whether the input character is a digit. However, the question arises regarding the appropriate input variable type: char or int.

Delving into C's Origins

To understand the choice of int input, we must delve into isdigit()'s origins in C. The function was designed to work with getchar(), which reads characters as int to provide both the character and an error code. Negative values indicate errors, while positive values represent character codes.

Signed vs Unsigned Char

This setup presents a dilemma with char, which can be either signed or unsigned depending on the implementation. Most systems adopt signed char by default, leading to potential clashes with getchar()'s error code convention (negative values).

Type Conversion for isdigit()

To address this issue, isdigit() expects an input int that represents an unsigned char. Therefore, the correct if condition should be:

if(isdigit((unsigned char)c))

Additional Considerations

Beyond the char-int conundrum, it's crucial to check for stream closure before accessing c. This ensures the stream is still valid and the value of c has been properly assigned.

Summary

While the initial code may not appear incorrect, it overlooks the intricacies of char's signedness and isdigit()'s input requirements. By casting the input to an unsigned char, we adhere to the function's contract and avoid potential undefined behavior.

The above is the detailed content of Should `isdigit()` Take a `char` or `int` Input?. For more information, please follow other related articles on the PHP Chinese website!