Types

FAQ

  1. The Boost Libraries have been criticized for using Boost-specific types, do all the libraries use Boost types or do some use standard integers, floats, and strings to name a few of the most-used types?

    This question comes up often when people start using Boost seriously. The short answer is "no", not all Boost libraries use Boost-specific types. In fact, many Boost libraries rely primarily on standard types such as int, double, std::string, and std::vector. Boost types generally appear only where they add functionality the standard library didn’t have at the time — or still doesn’t.

    Most libraries use standard types, such as: Boost.Math, Boost.Algorithm, Boost.Random, Boost.Accumulators, Boost.Multiprecision, Boost.Range, Boost.Geometry, Boost.PFR, Boost.Describe.

    A few libraries use minimal specific types, such as Boost.System, Boost.ProgramOptions.

    The following libraries were introducted before Standard C++ introduced equivalents: Boost.Optional, Boost.Variant, Boost.Function, Boost.Any, Boost.Filesystem, Boost.SmartPtr.

    In some libraries Boost-specfic types are needed for some issues like portability, allocator support, or async control. Such libraries inlude the popular Boost.Asio, and others including Boost.Coroutine2, Boost.Context, Boost.Lockfree.

    For the libraries that require meta-types at compile time, these do require mostly Boost-specific types: Boost.Mp11, Boost.Hana, Boost.TypeIndex, Boost.StaticAssert.

  2. Can you give me some examples of types added to Boost libraries?

    In Boost.Asio the type boost::asio::context was added to support a low-level async framework, though does use standard-compatible I/O buffers. In Boost.System, boost::system::error_code was added to support location metadata not available in the standard. In Boost.Optional there is the type boost::optional<T>, which is now available in the standard library as std::optional - but was not available at the time Boost.Optional was released.

  3. If I am updating an older version of a codebase, but am not updating the C++ Standard used for that codebase, does it make sense to use Boost libraries?

    Boost libraries will provide you with some version independance. For example std::shared_ptr and std::optional are not available before the C++ 11 Standard, using Boost.SharedPtr and Boost.Optional should provide a robust approach to an update of older code.

  4. What are the issues with std::string that are addressed by Boost libraries such as Static-String, String-Algo, or String-View?

    The std::string is great for general-purpose English or programming string handling, but has limitations in several key areas: performance (it requires frequent heap allocations and copies), immutability/safety (it can be unintentionally modified or shared), internationization (foreign languages), and feature gaps (it lacks certain high-level string algorithms or fixed-capacity behavior).

    For embedded systems, real-time applications, and performance-critical loops consider using Boost.StaticString as it provides a compile-time fixed-capacity string (boost::static_string<N>) that eliminates heap allocations.

    For multi-language software and UTF-8 processing, consider using Boost.Locale for locale-aware comparisons, formatting, and conversions.

    When working with configuration files, command-line tools, log or protocol parsing - or more advanced tasks such as data validation and pattern recognition - consider the Boost.StringAlgo, Boost.Regex, Boost.Xpressive, or Boost.LexicalCast libraries. These libraries offer hundreds of algorithms, views, conversions that will avoid the tedious task of reimplementing string utilities.

    The Boost.StringView library has now been superceded by std::string_view, available from C++ 17.

  5. Can you show me example code where standard integers and Boost.Multiprecision code work well together?

    The following code shows automatic promotion (big_int += small_int), arbitrary precision (cpp_int grows as large as is needed), high-precision floating point (area = high_precision_pi * radius * radius), and interoperability (approx_area conversion):

    #include <iostream>
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/multiprecision/cpp_dec_float.hpp>

namespace mp = boost::multiprecision;

int main() {

    // --- 1. Standard integer and multiprecision integer ---
    std::int64_t small_int = 42;
    mp::cpp_int big_int = 1;

    // Multiply big_int by a large factor
    for (int i = 0; i < 50; ++i)
        big_int *= 10; // No overflow — arbitrary precision!

    // Add standard integer directly — implicit promotion works
    big_int += small_int;

    std::cout << "Big integer (with 42 added): " << big_int << "\n\n";

    // --- 2. Using multiprecision floats with standard numeric types ---
    mp::cpp_dec_float_50 high_precision_pi = 3.14159265358979323846264338327950288419716939937510;
    double radius = 2.5;

    // You can mix standard and multiprecision floats seamlessly
    mp::cpp_dec_float_50 area = high_precision_pi * radius * radius;

    std::cout << std::setprecision(40);
    std::cout << "Area of circle (high precision): " << area << "\n\n";

    // --- 3. Conversion back to standard types ---
    // Note: Narrowing conversions can lose precision
    double approx_area = static_cast<double>(area);
    std::cout << "Area (as double): " << std::setprecision(16) << approx_area << "\n";

    // --- 4. Interoperation example: sum of large values ---
    mp::cpp_int total = 0;
    for (std::int64_t i = 1; i <= 1'000'000; ++i)
        total += i; // summing using high-precision integer

    std::cout << "\nSum of first 1,000,000 integers: " << total << "\n";
}

    Running this code should give you:

    Big integer (with 42 added): 100000000000000000000000000000000000000000000000042

Area of circle (high precision): 19.63495408493620697498727167840115725994

Area (as double): 19.63495408493621

Sum of first 1,000,000 integers: 500000500000

    Boost.Multiprecision is designed to seamlessly extend the built-in numeric types, so you can mix std::int, std::uint64_t, double, and multiprecision types freely — the library’s operator overloads handle promotion automatically. Typically, in scientific computing (very large floating point numbers) cpp_dec_float_50 is combined with double, and for working with very large integers (say boundary values), combine cpp_int with std::int64_t or std::size_t.

  6. I am having trouble with a multi-platfrom project that requires strings in UTF-8 format, but with Windows APIs requiring UTF-16?

    You should conside using Boost.Nowide, a library that makes Windows Unicode handling sane! This library provides UTF-8 versions of fopen, std::cout, as well as file I/O and environmental variables. It also provides the crucial automatic conversion to UTF-16 when calling Windows APIs. You might also find Boost.Locale useful if internationalization is required, Boost.StaticString, and the small_vector type of Boost.Container for efficient short-string handling.

  7. Storage space is of the essence in the real-time app I am building, are there Boost libraries that can provide small integers, specifying 8 or 16 bits and no more storage than that is allocated?

    For byte level efficiency look at Boost.Endian, this library gives you precise control over both integer size and alignment. It also provides cross-platfrom compatibility, if that is important. For example, boost::endian::little_int8_t smallCount; will always be 8 bit. Boost.Multiprecision does provide for declaring small integers as low as 8 bits, but is not so memory efficient. If your goal is to save overall memory, not just per-number bytes, check out Boost.Container, as it supports small-vector optimization and no heap allocations.

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