To read an int using scanf we use:
scanf("%d",&i);
What if i is long not int??
Note: when using %d with long it gives me an irritating warning..
Thanks!
views:
265answers:
4
+1
A:
scanf("%ld", &i);
You can also use "%Ld" for a long long (and depending on your compiler, sometimes also "%lld").
Take a look at the Conversions section of the scanf man page for more. (Just Google it if your system doesn't have manpages).
Vineet
2010-05-17 20:16:45
And doesn't that same man page say that the things you are reading into need to be passed to scanf as pointers?
anon
2010-05-17 20:28:29
For `long long (int)`, "%lld" is standard (the "L" modifier is meant for `long double`, so "%Ld" isn't standard, though I don't doubt that some implementations allow it). BSD flavours once used the "q" length modifier for a "quadword", which is just a 64-bit value, and I'm reasonably sure it is still accepted in some BSD-based implementations. Microsoft created the "I64" and "I32" length modifiers to specify a 64-bit and a 32-bit integer respectively, so "%I64d" would be valid in that case. In other words, `long long` is a mess of confusion when it comes to the formatted I/O functions. :P
Dustin
2010-05-17 20:59:43
+3
A:
Just use
long l;
scanf("%ld", &l);
it gives me an irritating warning..
That warning is quite right. This is begging for stack corruption.
jpalecek
2010-05-17 20:16:53
Whereas your code simply gives undefined behaviour. You need to give scanf the address of the variable being read into.
anon
2010-05-17 20:19:40
To add to Neil's answer, you can't rely on something like "%d" to read a `long int` because that specifies an `int` rather than a `long (int)`. Not only that, `int` on some 64-bit systems is 32 bits in size while `long (int)` is 64 bits in size. In other words, you'd be reading a 32-bit integer into what is meant to be a 64-bit storage location. An example would be reading 2147483649. Since the 32-bit value is read into a 64-bit location, the other 32 bits are left with whatever values were present, so you might get something like 6442450945 if you had 4294967296 stored in there originally.
Dustin
2010-05-17 20:47:20
+1
A:
Each conversion specifier expects its corresponding argument to be of a specific type; if the argument's type does not match the expected type, then the behavior is undefined. If you want to read into a long with scanf(), you need to use the %ld conversion specifier:
long i;
scanf("%ld", &i);
Check the online draft C standard (.pdf file), section 7.19.6.2, paragraph 11 for a complete listing of size modifiers and expected types.
John Bode
2010-05-17 21:11:12