C:\Users\bion\Desktop>type test.cpp
#include <assert.h>
#include <regex>
#include <stddef.h>
#include <stdio.h>
#include <string>

void test(size_t number) {
  printf("Testing %zu...\n", number);
  try {
    std::string s(number, 'a');
    const auto pattern = "a{" + std::to_string(number) + "}";
    std::regex r(pattern.c_str());
    std::smatch results;
    assert(regex_match(s, results, r));
    assert(results.size() == 1);
    const auto &firstResult = results[0];
    assert(static_cast<size_t>(firstResult.second - firstResult.first) ==
           number);
  } catch (const std::exception &e) {
    puts(e.what());
  }
}

int main() {
  test(0xFFFF'FFFFull);
  test(0x1'0000'0000ull);
  puts("pass");
}

C:\Users\bion\Desktop>cl /EHsc /W4 /WX /nologo /O2 .\test.cpp
test.cpp

C:\Users\bion\Desktop>.\test.exe
Testing 4294967295...
regex_error(error_complexity): The complexity of an attempted match against a regular expression exceeded a pre-set level.
Testing 4294967296...
Assertion failed: regex_match(s, results, r), file .\test.cpp, line 14

C:\Users\bion\Desktop>