如何找出，用户输入包含C中的非ASCII字符

Question

I'm reading user input with fgets() and I'm checking if there are some non allowed symbols.

If user types "š" for example, I will notice it, because value of "š" is higher then 127. But when user types "ασδφ" or "жщдф", my code won't work, because these symbols are completely ignored and replaced by "?".

My code:

char input[100];
fgets(input, 100, stdin);
for (int i = 0; i < strlen(input) - 1; i++)
{
    /// Check, if input[i] is ASCII symbol
}

When user types "š", in variable input will be "š". But when user types "щ", int variable input will be "?" and question mark is valid ASCII character.

How to fix it?

EDIT:

Operating system: Windows 10

IDE: Visual Studio 2015

Code:

for (size_t i = 0; i < strlen(input); i++)
{
    printf("%c %d\n", input[i], input[i]);
    if (input[i] < 0/* || input[i] > 127*/)
    {
        error = 4;
        break;
    }
}

If I pause a program, content of array input for user input "ασδφ" is 63, 63, 63, 63, 10.

EDIT 2:

Now I'm totaly confused. I tried compiling and running on Ubuntu, everything worked fine. But on Windows it is still replacing non ASII symbols with questions marks. Any idea how to get it work on Windows?

Answer 1

I think you should use isascii(int ch) function defined in ctype.h header:

#include <ctype.h>

char input[100];
fgets(input, 100, stdin);
for (int i = 0; i < strlen(input) - 1; i++)
{
    if (isascii((int)input[i]) {
        /* If ASCII */
    } else {
       /*If non-ASCII */
    }
}

Answer 2

You can also use this :

#include <stdio.h>

main(){
char input[100];
fgets(input, 100, stdin);
for (int i = 0; i < strlen(input) - 1; i++)
{
    if(input[i]<128 && input[i]>0)
        printf("\nASCII Value");
    else
        printf("\nNot an ASCII Value");
}
}

Answer 3

It is hard to tell from the details you've provided, but I do not think the problem is in your code. When you mentioned that it works on Ubuntu, that hints that you are experiencing an encoding issue with your console.

If stdin is a file handle this shouldn't be an issue, but it sounds like you are trying to use stdin from the command line and copy/pasting input. Windows command prompt will convert unicode characters to '?' if they are not supported by your console font. See this question and the accepted answer for more information:

What encoding/code page is cmd.exe using?