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Fix std::showbase vs std::noshowbase #371

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mborland merged 3 commits into from
Mar 24, 2026
+32 −12
Merged

Fix std::showbase vs std::noshowbase #371

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da44c61
Fix and add additional testing of ostream values
mborland Mar 24, 2026
8150b07
Only append base when the flags say so
mborland Mar 24, 2026
5517b6b
Improve streaming docs
mborland Mar 24, 2026
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6 changes: 4 additions & 2 deletions doc/modules/ROOT/pages/stream.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,9 @@ The following flags from `<ios>` are supported for both streaming directions:
- `std::oct` - Octal Numbers
- `std::dec` - Decimal Numbers
- `std::hex` - Hexadecimal Numbers
- `std::uppercase` - Upper Case Formatting (e.g. 0XFFFF)
- `std::nouppercase` - Lower Case Formatting (e.g. 0xffff)
- `std::uppercase` - Upper Case Formatting (e.g. FFFF)
- `std::nouppercase` - Lower Case Formatting (e.g. ffff)
- `std::showbase` - Adds a leading base for hex or oct numbers (e.g. 0xffff)
- `std::noshowbase` - Removes the leading base for hex or oct numbers (e.g. ffff)

See the xref:examples.adoc#examples_io[IO streaming example] for usage demonstrations.
17 changes: 10 additions & 7 deletions include/boost/int128/iostream.hpp
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Expand Up @@ -124,14 +124,17 @@ auto operator<<(std::basic_ostream<charT, traits>& os, const LibIntegerType& v)

auto first {detail::mini_to_chars(buffer, v, base, uppercase)};

if (base == 8)
if (flags & std::ios_base::showbase)
{
*--first = '0';
}
else if (base == 16)
{
*--first = uppercase ? 'X' : 'x';
*--first = '0';
if (base == 8)
{
*--first = '0';
}
else if (base == 16)
{
*--first = uppercase ? 'X' : 'x';
*--first = '0';
}
}

BOOST_INT128_IF_CONSTEXPR (!std::is_same<charT, char>::value)
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21 changes: 18 additions & 3 deletions test/test_stream.cpp
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Expand Up @@ -89,23 +89,38 @@ void test_ostream()
std::stringstream hex_out;
hex_out.flags(std::ios_base::hex);
hex_out << hex_val;
BOOST_TEST_CSTR_EQ(hex_out.str().c_str(), "0xff");
BOOST_TEST_CSTR_EQ(hex_out.str().c_str(), "ff");

// 32-bit windows does not set the flags correctly in CI
#ifndef _M_IX86

std::stringstream hex_out_base;
hex_out_base.flags(std::ios_base::hex | std::ios_base::showbase);
hex_out_base << hex_val;
BOOST_TEST_CSTR_EQ(hex_out_base.str().c_str(), "0xff");

std::stringstream hex_out_upper;
hex_out_upper.flags(std::ios_base::hex | std::ios_base::uppercase);
hex_out_upper << hex_val;
BOOST_TEST_CSTR_EQ(hex_out_upper.str().c_str(), "0XFF");
BOOST_TEST_CSTR_EQ(hex_out_upper.str().c_str(), "FF");

std::stringstream hex_out_upper_base;
hex_out_upper_base.flags(std::ios_base::hex | std::ios_base::uppercase | std::ios_base::showbase);
hex_out_upper_base << hex_val;
BOOST_TEST_CSTR_EQ(hex_out_upper_base.str().c_str(), "0XFF");

#endif

T octal_val {04};
std::stringstream octal_out;
octal_out.flags(std::ios_base::oct);
octal_out << octal_val;
BOOST_TEST_CSTR_EQ(octal_out.str().c_str(), "04");
BOOST_TEST_CSTR_EQ(octal_out.str().c_str(), "4");

std::stringstream octal_out_upper;
octal_out_upper.flags(std::ios_base::hex | std::ios_base::showbase);
octal_out_upper << octal_val;
BOOST_TEST_CSTR_EQ(octal_out.str().c_str(), "4");

BOOST_INT128_IF_CONSTEXPR (std::is_same<T, boost::int128::uint128_t>::value)
{
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