Re: Things to Avoid in C/C++ -- scanf / epilogue, Part 9

WaltP · #1 01-Oct-2005, 05:24

I just posted a GID Community blog entitled: Things to Avoid in C/C++ -- scanf / epilogue, Part 9.

Quote:

scanf() / So what's a programmer to do?

scanf() is not designed for production code, but for creating test programs to see if other aspects of the program are working. scanf() will replace the complicated input routines so that other modules can be exercised and perfected. Then the scanf() is replaced with the real input function that gets the actual data from a file, a device, wherever the actual data is stored. read more...

Please let me know what you think.

This is an auto-generated message posted by GIDNetwork™ on behalf of the author.

GeertVc · #2 14-Sep-2008, 11:42

Quote:

Originally Posted by WaltP

Please let me know what you think.

In the last example, I see this:

CPP / C++ / C Code:

int  getCharacter()
{
    int ch;         // define the character
    do              // loop until a good character is read
    {
        ch = getchar();         // read a character
    } while ((ch <= 0x20) ||    // check above SPACE
             (ch >= 0x7F)       // check below the last 
            );                  //    ASCII char
    return ch;
}

Should the signs in the while() condition not be reversed?

Best rgds,
--Geert

ocicat · #3 14-Sep-2008, 13:13

Quote:

Originally Posted by GeertVc

Should the signs in the while() condition not be reversed?

If you look at a chart of ASCII values:

http://www.asciitable.com/

...you will see that characters below 0x20 are considered non-printable, & 0x7f represents the upper boundary. Given that the code uses a do-while loop, the loop will repeat while the condition is true. In other words, as if the character read is not printable or above DEL, get another character. If the character read is a printable character, exit the loop & return the character as the return value of the function.

Basically, the function ensures that the keypress received as input is a printable ("good") character. If it is not, then repeat ad infinitum until a printable character is received.

You can always compile the code yourself in a test application to verify its behaviour.

GeertVc · #4 15-Sep-2008, 11:08

Quote:

Originally Posted by ocicat

If it is not, then repeat ad infinitum until a printable character is received.

You're right. I completely missed the way the do-while construction has been made...

Best rgds,
--Geert

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