Why do C compilers specify long to be 32-bit and long long to be 64-bit?

The c standard have NOT specified the bit-length of primitive data type, but only the least bit-length of them. So compilers can have options on the bit-length of primitive data types. On deciding the bit-length of each primitive data type, the compiler designer should consider the several factors, including the computer architecture.

here is some references: http://en.wikipedia.org/wiki/C_syntax#Primitive_data_types

Yes, it does make sense, but Microsoft had their own reasons for defining "long" as 32-bits.

As far as I know, of all the mainstream systems right now, Windows is the only OS where "long" is 32-bits. On Unix and Linux, it's 64-bit.

All compilers for Windows will compile "long" to 32-bits on Windows to maintain compatibility with Microsoft.

For this reason, I avoid using "int" and "long". Occasionally I'll use "int" for error codes and booleans (in C), but I never use them for any code that is dependent on the size of the type.

For historical reasons. For a long time (pun intended), "int" meant 16-bit; hence "long" as 32-bit. Of course, times changed. Hence "long long" :)

PS:

GCC (and others) currently support 128 bit integers as "(u)int128_t".

PPS:

Here's a discussion of why the folks at GCC made the decisions they did:

http://www.x86-64.org/pipermail/discuss/2005-August/006412.html