What's the difference between long long and long

c++ int long-integer

44,137

Solution 1

Going by the standard, all that's guaranteed is:

int must be at least 16 bits
long must be at least 32 bits
long long must be at least 64 bits

On major 32-bit platforms:

int is 32 bits
long is 32 bits as well
long long is 64 bits

On major 64-bit platforms:

int is 32 bits
long is either 32 or 64 bits
long long is 64 bits as well

If you need a specific integer size for a particular application, rather than trusting the compiler to pick the size you want, #include <stdint.h> (or <cstdint>) so you can use these types:

int8_t and uint8_t
int16_t and uint16_t
int32_t and uint32_t
int64_t and uint64_t

You may also be interested in #include <stddef.h> (or <cstddef>):

size_t
ptrdiff_t

Solution 2

long long does not exist in C++98/C++03, but does exist in C99 and c++0x.

long is guaranteed at least 32 bits.

long long is guaranteed at least 64 bits.

Solution 3

To elaborate on @ildjarn's comment:

And they both don't work with 12 digit numbers (600851475143), am I forgetting something?

The compiler looks at the literal value 600851475143 without considering the variable that you're assigning it to/initializing it with. You've written it as an int typed literal, and it won't fit in an int.

Use 600851475143LL to get a long long typed literal.

44,137

Author by

Hikari Iwasaki

Programming Student in FRC

Updated on July 09, 2022

Comments

Hikari Iwasaki almost 2 years
What's the difference between long long and long? And they both don't work with 12 digit numbers (600851475143), am I forgetting something?
```
#include <iostream>
using namespace std;

int main(){
  long long a = 600851475143;
}
```
- ildjarn almost 13 years
  
  Make that long long a = 600851475143LL; and it should work.
- Mahmoud Gabr almost 3 years
  
  @ildjarn Why would I need to to specify the format using the (LL) postfix, when I have already specified it with a (long long) when declaring the variable?
Hikari Iwasaki almost 13 years

what do you mean by the "long is either 32 or 64 bits"? Can it change its bits?
Joey Adams almost 13 years

@Hikari Iwasaki: It depends on the target. For example, if you're compiling on Windows, it might be 32 bits, while on Linux x86-64, it might be 64 bits. Types don't change sizes at run-time.
Alexis Wilke over 2 years

And g++ even has an __int128 type, to extend the list...