How does long long syntax work when int int doesn't in C++?

Question

I was wondering if long long specifies a single datatype then why don't things like int int work? I meant obviously that's not a data type but there is a long data type. Essentially what I'm asking is:

int a = 0; //okay
long b = 0; //still fine
long long c = 0; //really long number but its okay....
int int d = 0; //error

why?

Answer 1

The difference between long long and int int is that long modifies a type, rather than being a type itself. long is really a shorthand for long int and long long a shorthand for long long int.

More specifically int is a type specifier, just like char or bool. long is a type modifier. Other type modifiers are unsigned and signed and short.

If one of the modifiers is missing then the type will fall back to a default. E.g. if there is no signed or unsigned then the type will be signed. If there is no short or long the default size depends on the compiler and the architecture.

Take a look at this table on Wikipedia for a full list of how different type specifiers and modifiers can be combined.

Edit:

In current versions of the C and C++ standards long and short are actually type specifiers in their own right. This doesn't change the way that things can be combined though.

Answer 2

You can specify a long integer that is longer than a long as long long.

But what would it mean to specify an integer that is more integer than int?

More precisely. In C++ you have type int, which is normally a 32-bit wide integer. You then have the modifiers short and long that can be used as illustrated by the following example:

#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
    cout << "short int:     " << sizeof(short int) << endl;
    cout << "short:         " << sizeof(short) << endl;
    cout << "int:           " << sizeof(int) << endl;
    cout << "long int:      " << sizeof(long int) << endl;
    cout << "long:          " << sizeof(long) << endl;
    cout << "long long int: " << sizeof(long long int) << endl;
    cout << "long long:     " << sizeof(long long) << endl;
}

On my Linux box, running g++ 4.7.2, this gives:

short int:     2
short:         2
int:           4
long int:      8
long:          8
long long int: 8
long long:     8

So:

• int is a 32-bit signed integer
• short int (abbreviated, short) is a 16-bit signed integer
• long int (abbreviated, long) is a 64-bit signed integer
• long long int (abbreviated, long long) is still a 64-bit signed integer on my architecture / compiler, but it is in the language to allow a longer integer type (e.g. 128 bit) on different architectures / compilers.

So, as Will has explained: in this context, long is a modifier that can be applied twice whereas int is not a modifier.