10 replies to this topic

[Moudi]

So i was snooping around and trying to find out what sscanf does, so okay its a better scanf

int a = sscanf(buffer, "%d", &n);

if (a != 1)
{
// user didn't input an integer in n ;
}

Now can someone please explain what the buffer is for ? And i've seen some sscanf's that are transfering stuff from buffer to other variables like sscanf(buffer, "%s %*s %d", &bla, &bla1, &bla2);

whats %*s.

Oh well thats all my questions ^_^

Thanks in advance for anyone that tries to help me

[dargueta]

Do you know what scanf is for? Because sscanf is exactly the same thing except it reads from a string, not STDIN. That's what the buffer is - the string it's reading from.

As far as %*s, that's a way of telling the scanf functions that the number of characters you want to read is specified in a variable. For example:

sscanf("%d %32s", &myint, mystring);

This tells sscanf that you want to read in an integer and at most 32 characters into mystring.

EDIT: I screwed up and got two format specifiers mixed up, so I removed this bit.

Edited by dargueta, 19 March 2010 - 01:39 PM.

[Moudi]

So lets say
char mystring[] = "Mouhammed age 12";
char string[10];
sscanf(mystring, "%9s %d", string, &age);

That will input Mouhammed in the string " string ", and 12 in the age integer ?

[dargueta]

No, unfortunately. (I got that confused with the %n specifier. Next time I'll double-check what I post.) In normal convention, the asterisk means "discard this input." Your format string should be like this:

sscanf(mystring, "%9s %*s %d",string,&age);

If you want to specify a variable size, you can use the 'a' modifier (note this is a GNU/C99 extension) to dynamically allocate a buffer. Important: you have to pass in a pointer to your char * pointer, not just your char * pointer. Take this as an example:

int age;
char *name;
const char *mystring = "Mouhammad age 12";

sscanf(mystring, "%as %*s %d", [U][B]&[/B][/U]name, &age);

// do something here with name

free(name);

Make sure you deallocate name or else you're going to leak memory and probably run out.

[dcs]

I generally don't advise using non-standard extensions: it will bite you in the ass some day.

[dargueta]

Ok...that's weird. I know I edited my first post...

[Moudi]

Well i'm sounding like pain in the ass i know but let me get this straight, i want to know what it accualy works, now i know how's its syntax..

[dargueta]

Oh, you mean you want to know the inner workings of sscanf?

[Moudi]

Yes please

[dargueta]

That's implementation-specific; everyone can pretty much do it their own way as long as they conform to the standards. You should be able to find the GNU implementation online somewhere with Google.

[dcs]

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