# Cannot print uint128\_t values

**URL:** <https://openfhe.discourse.group/t/cannot-print-uint128-t-values/2235>\
**Category:** Library Questions\
**Tags:** bugs\
**Created:** [December 11, 2025, 2:25pm UTC](https://openfhe.discourse.group/t/cannot-print-uint128-t-values/2235 "2025-12-11T14:25:23Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![narger](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/narger/32/420_2.png) [@narger](https://openfhe.discourse.group/u/narger)\
**Post date:** [December 11, 2025, 2:25pm UTC](https://openfhe.discourse.group/t/cannot-print-uint128-t-values/2235/1 "2025-12-11T14:25:23Z")

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Hi, just a quick issue (I would have opened it on GitHub, but apparently only contributors can)."  
Trying to print a `uint128_t` value causes the following compilation error:

```auto
error: use of overloaded operator '<<' is ambiguous (with operand types 'ostream' (aka 'basic_ostream<char>') and 'uint128_t' (aka 'unsigned __int128'))
   32 | std::cout << x;

```

I guess the definition for `<<` is missing, or something like that. The bug is easily replicable, simply write

```auto
uint128_t x = 10;
std::cout << x;

```

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**Author:** ![dsuponitskiy-duality](https://avatars.discourse-cdn.com/v4/letter/d/c68b51/32.png) [@dsuponitskiy-duality](https://openfhe.discourse.group/u/dsuponitskiy-duality)\
**Post date:** [December 16, 2025, 3:28pm UTC](https://openfhe.discourse.group/t/cannot-print-uint128-t-values/2235/2 "2025-12-16T15:28:22Z")

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uint128\_t/\_\_uint128\_t is not a standard C++ type, it’s a compiler extension. that’s why std::cout does not natively support it.  
you can print it with a custom function similar to this:

```cpp
std::string to_string_uint128(__uint128_t v) {
    if (v == 0)
        return "0";

    std::string s;
    while (v > 0) {
        s.push_back((v % 10) + 48);
        v /= 10;
    }

    std::reverse(s.begin(), s.end());
    return s;
}

```

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<div class="post-metadata">

**Author:** ![narger](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/narger/32/420_2.png) [@narger](https://openfhe.discourse.group/u/narger)\
**Post date:** [December 16, 2025, 3:40pm UTC](https://openfhe.discourse.group/t/cannot-print-uint128-t-values/2235/3 "2025-12-16T15:40:28Z")

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thank you very much:) i was able to print it eventually, just created this to report the problem