Zimano Zimano - 1 month ago 8x
C Question

uint128_t does not name a type

I am porting some code from C to C++. During the conversion I encountered:

does not name a type

My compiler: gcc version 5.2.1

My operating system: Ubuntu 15.1

First and foremost; this compiled fine as C.
I thought this would be resolved by including
but it has not. So far I have not tried anything else since there doesn't seem to be any other information on this error (for example).
is used throughout the entire program and is essential for the build, therefore I can not remove it, or use a different integer type.

The code that sparks the error is widespread, for example:

union {
uint16_t u16;
uint32_t u32;
uint128_t u128;
} value;

Is there any way to either define
or update my compiler to handle it correctly?


GCC has builtin support for the types __int128, unsigned __int128, __int128_t and __uint128_t (the last two are undocumented). Use them to define your own types:

typedef __int128 int128_t;
typedef unsigned __int128 uint128_t;

Alternatively, you can use __mode__(TI):

typedef int int128_t __attribute__((mode(TI)));
typedef unsigned int uint128_t __attribute__((mode(TI)));

Quoting the documentation:


“Tetra Integer” (?) mode represents a sixteen-byte integer.

Sixteen byte = 16 * CHAR_BIT >= 128.