Thread: fgets - It will always return [string] + newline + nul?

Sorry. Im still a bit upset over input validation.

Consider the following:

Code:

 fgets(BUF,10,stdin);

BUF is supposed to take in 10 chars. But only 9 chars will be readable by us. Since the last char will always be a '\0'.

Defination of fgets:

Reads characters from stream and stores them in string until (num -1) characters have been read or a newline or EOF character is reached, whichever comes first.
A newline character ends reading but is considered a valid character and included in the new string.
A null character is always appended at the end of the resulting string.

So there are 3 conditions to monitor:

1. A user keys in exactly (num-1) chars.
2. A user keys in more than (num-1) chars.
3. A user keys in less than (num.1) chars.

Condition 1:
If a user keys in the following:

TAEKWONDO

and hits a carriage return; what is actually being taken into the system is:

TAEKWONDO\n\0

So BUF will be TAEKWONDO\0 ? Since BUF has already read (num-1) chars? What happened to the \n then?

Condition 2:
But if a user keys in the following:

TAEKWONDOTAEKWONDOTAEKWONDO

and hits a carriage return; what is being captured by the system is:

TAEKWONDOTAEKWONDOTAEKWONDO\n\0

So BUF will be TAEKWONDO\0 also? The remaining chars will be stored in the buffer?

Condition 3:

If a user keys in the following:

HELLO

and hits a carriage return; what is being captured by the system is:

HELLO\n\0

BUF will be exactly HELLO\n\0 ?

Im getting confused. Can someone enlighten please? Thanks

Oh ok. Thanks! I shall play with it again.

But about backspaces '\b'?

Are \b being taken in also? And what about tabs '\t' ?

Are they considered to be one character also?

Originally Posted by Salem

> What happened to the \n then?
> The remaining chars will be stored in the buffer?
You'll get them on the next fgets() call.
Basically, if you don't find a \n, then expect a long line and deal with it accordingly.

oh ok..Hmm...I just wrote and tested this and it seems fine in my outputs.
it managed to clear unwanted buffer (the extra buffer that exceeded the desire char length) and the irritating \n at end of the input (if any)

Is this foolproof enough?

Please advise.

Code:

         fgets(buf,10,stdin);
         if(buf[strlen(buf)-1]!='\n')
            while((ch=getchar())!='\n' && ch!=EOF); 
         else
            buf[strlen(buf)-1]='\0';

Originally Posted by stevong

Code:

         fgets(buf,10,stdin);
         if(buf[strlen(buf)-1]!='\n')
            while((ch=getchar())!='\n' && ch!=EOF); 
         else
            buf[strlen(buf)-1]='\0';

You don't really need to walk the string twice. You could capture the result of strlen in a variable and use it again, like in the foo, here.