Re: Things to Avoid in C/C++ -- gets() , Part 1

WaltP · #1 05-Dec-2004, 23:28

I just posted a GID Community blog entitled: Things to Avoid in C/C++ -- gets() , Part 1.

Quote:

C/C++ programmers are allowed to do some things they shouldn't. We are given functions that are supposed to be useful but aren't because of hidden faults, or taught ways to do things that are bad, wrong, not necessary. These posts will discuss many of these as time goes on.

The code in this collection of electronic bits is specifically written in C. I'm using the free Borland 5.5 compiler for the code. For any code that is designed to show the errors, your results may be a little different. But rest assured, the problem exists in many if not all compilers. And if most compilers show these anomalies, wouldn't you rather not use the feature even if it works on your current compiler? read more...

Please let me know what you think.

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

WaltP · #2 09-Dec-2004, 21:58

Things to avoid in C/C++
void main()

main() is an integer function, and should be specified as such. Now I can get into long-winded explanation of why, but it's already been done, with examples.

I first turn your attentopn to this article by Steve Summit: http://www.eskimo.com/~scs/readings/...in.960823.html. He explains what could happen and why. How the improper form started and why it's been allowed to continue.

The second is http://users.aber.ac.uk/auj/voidmain.shtml by Alun Jones, with a real world example of an error.

Another good explanation is at http://home.att.net/~jackklein/ctips01.html#int_main.

So the bottom line is void main()
1) is wrong according to the standards.
2) is not guaranteed to work properly.
3) may cause problems for the operating system.

seprich · #3 15-Jun-2007, 02:03

Hi,

In your blog:
GIDNetwork > Things to Avoid in C/C++ -- gets() , Part 1

there is the following example:

Quote:

CPP / C++ / C Code:

puts("Enter some characters:");
fgets(b2, 5, stdin);  // 5 is the size of buffer b2
if (b2[strlen(b2)-1] == '\n') 
{   // full input line read
    b2[strlen(b2)-1] = '\0';  // remove the new-line
}
else
{   // parial input line read
    b2[0] = 0;  // empty the b2 buffer
    do
    {   // loop until the new-line is read
        fgets(dummy, 50, stdin);
        strcat(b2, dummy);  // Save input but be sure
                            // sure to test your buffer size
    } while (dummy[strlen(dummy)-1] != '\n');
}

where the "b2[0] = 0;" will cause the 4 chars already read to the buffer to be lost. Probably supposed to be "b2[4] = 0;"

Also if "fgets(b2, 5, stdin); // 5 is the size of buffer b2" we cannot catenate the dummy to the b2. Rather in the spirit of the article I understood that we just want to clean the input stream by reading to dummy and that's all. "dummy" just acts as trash bin.

WaltP · #4 15-Jun-2007, 11:51

If you read the description carefully, is says

Quote:

To deal with both options at once to either remove the trailing '\n' or clear the buffer, whichever situation exists, define a dummy buffer of say 50 characters (you choose the size) and use this code:

You'll also see that the code itself says:

CPP / C++ / C Code:

else
{   // parial input line read
    b2[0] = 0;  // empty the b2 buffer

The code works as advertised.

Of course, you could just leave the buffer as you suggest, it's just not what was designed.

it career · #5 20-Jun-2007, 01:55

Quote:

Originally Posted by WaltP

Things to avoid in C/C++
void main()

main() is an integer function, and should be specified as such. Now I can get into long-winded explanation of why, but it's already been done, with examples.

I first turn your attentopn to this article by Steve Summit: www.eskimo.com. He explains what could happen and why. How the improper form started and why it's been allowed to continue.

The second is users.aber.ac.uk by Alun Jones, with a real world example of an error.

Another good explanation is at home.att.net.

So the bottom line is void main()
1) is wrong according to the standards.
2) is not guaranteed to work properly.
3) may cause problems for the operating system.

My compiler throws an error in case i declare main as void. So I guess this is taken care by compiler now.

mikhail · #6 21-Jun-2007, 12:13

Quote:

Originally Posted by it career

My compiler throws an error in case i declare main as void. So I guess this is taken care by compiler now.

Varies from compiler to compiler.

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