Frequently Asked Questions

This section contains answers to the common questions that new developers to Boost often have.

Compatibility

  1. Can I use Boost with my existing C++ project?

    Yes, Boost is designed to work with your existing C++ code. You can add Boost libraries to any project that uses a compatible C++ compiler.

  2. Can I use Boost libraries with the new C++ standards?

    Yes, Boost libraries are designed to work with modern C++ standards including C++11, C++14, C++17, and C++20.

  3. What flavors of Linux are supported by the Boost libraries?

    Boost libraries are generally compatible with most Linux distributions, provided that the distribution has an up-to-date C++ compiler. This includes:

    • Ubuntu

    • Fedora

    • Debian

    • CentOS

    • Red Hat Enterprise Linux

    • Arch Linux

    • openSUSE

    • Slackware

    • Gentoo

    • macOS

  4. How can I be sure that a library I want to use is compatible with my OS?

    While Boost strives to ensure compatibility with a wide range of compilers and systems, not every library may work perfectly with every system or compiler due to the inherent complexities of software. The most reliable source of information is the specific Boost library’s documentation.

Debugging

  1. What support does Boost provide for debugging and testing?

    Boost provides boost:test for unit testing, which can be an integral part of the debugging process. It also provides the Boost.Stacktrace library that can be used to produce useful debug information during a crash or from a running application.

  2. How do I enable assertions in Boost?

    Boost uses its own set of assertion macros. By default, BOOST_ASSERT is enabled, but if it fails, it only calls abort(). If you define BOOST_ENABLE_ASSERT_HANDLER before including any Boost header, then you need to supply boost::assertion_failed(msg, code, file, line) and boost::assertion_failed_msg(msg, code, file, line) functions to handle failed assertions.

  3. How can I get a stack trace when my program crashes?

    You can use the Boost.Stacktrace library to obtain a stack trace in your application. You can capture and print stack traces in your catch blocks, in signal handlers, or anywhere in your program where you need to trace the execution path.

  4. Can I use Boost with a debugger like GDB or Visual Studio?

    Yes, Boost libraries can be used with common debuggers like GDB or Visual Studio. You can set breakpoints in your code, inspect variables, and execute code step by step. Boost doesn’t interfere with these debugging tools.

  5. Are there any debugging tools specifically provided by Boost?

    Boost doesn’t provide a debugger itself. The libraries tend to make heavy use of assertions to catch programming errors, and they often provide clear and detailed error messages when something goes wrong.

  6. What are best practices when using Boost Asserts?

    Boost provides the assertion boost::assert. Best practices when using this are:

    • Use Assertions for Debugging and Development: Boost assertions should primarily be used during the debugging and development phase of your application. Assertions are designed to catch programming errors, not user errors.

    • Assert Conditions That Should Never Occur: You should only assert conditions that you believe can never occur during normal operation of your application. If there’s a chance that a condition may occur, handle it as an exception or error rather than asserting.

    • Provide Meaningful Assert Messages: Boost assertions allow you to provide a message alongside your assertion. Use this feature to provide meaningful context about why an assertion failed.

    • Consider Performance Impact: Boost assertions can slow down your application. In performance-critical code, consider disabling them in the production version of your application.

  7. What is the recommended approach to logging, using boost::log?

    • Use Severity Levels: Boost.Log supports severity levels, which you can use to categorize and filter your log messages. This can help you control the amount of log output and focus on what’s important.

    • Provide Context:https://www.boost.org/libs/log[Boost.Log] allows you to attach arbitrary data to your log messages, such as thread IDs, timestamps, or file and line information. Use this feature to provide context that can help you understand the state of your application when the log message was generated.

    • Use Asynchronous Logging: If logging performance is a concern, consider using the asynchronous logging feature. This allows your application to continue executing while log messages are processed in a separate thread.

    • Format Your Log Output: Boost.Log supports customizable log formatting. Use this feature to ensure that your log output is easy to read and contains all the information you need.

    • Handle Log Rotation: If your application produces a lot of log output, consider setting up log rotation, which is supported. This ensures that your log files don’t grow indefinitely.

Libraries

  1. What are smart pointers in Boost?

    Smart pointers are a feature of C++ that Boost provides in its Boost.SmartPtr library. They are objects that manage the lifetime of other objects, automatically deleting the managed object when it is no longer needed. See the Smart Pointers section.

  2. Does Boost provide a testing framework?

    Yes, Boost.Test is the unit testing framework provided by Boost. It includes tools for creating test cases, test suites, and for handling expected and unexpected exceptions. Refer to Testing and Debugging.

  3. What is Boost.Asio?

    Boost.Asio is a library that provides support for asynchronous input/output (I/O), a programming concept that allows operations to be executed without blocking the execution of the rest of the program.

  4. What is Boost.MP11?

    Boost.Mp11 (MetaProgramming Library for C++11) is a Boost library designed to bring powerful metaprogramming capabilities to C++ programs. It includes a variety of templates that can be used to perform compile-time computations and manipulations. Refer to Metaprogramming.

  5. Does Boost provide a library for threading?

    Yes, Boost.Thread provides a C++ interface for creating and managing threads, as well as primitives for synchronization and inter-thread communication.

  6. What is the Boost Spirit library?

    Boost.Spirit is a library for building recursive-descent parsers directly in C++. It uses template metaprogramming techniques to generate parsing code at compile time.

  7. I like algorithms, can you pique my interest with some Boost libraries that support complex algorithms?

    Boost libraries offer a wide range of algorithmic and data structure support. Here are five libraries that you might find interesting:

    • Boost.Graph: This library provides a way to represent and manipulate graphs. It includes algorithms for breadth-first search, depth-first search, Dijkstra’s shortest paths, Kruskal’s minimum spanning tree, and much more.

    • Boost.Geometry: This library includes algorithms and data structures for working with geometric objects. It includes support for spatial indexing, geometric algorithms (like area calculation, distance calculation, intersections, etc.), and data structures to represent points, polygons, and other geometric objects.

    • Boost.Multiprecision: If you need to perform computations with large or precise numbers, this library can help. It provides classes for arbitrary precision arithmetic, which can be much larger or more precise than the built-in types.

    • Boost.Compute: This library provides a C++ interface to multi-core CPU and GPGPU computing platforms based on OpenCL. It includes algorithms for sorting, searching, and other operations, as well as containers like vectors and deques.

    • Boost.Spirit: If you’re interested in parsing or generating text, this library includes powerful tools based on formal grammar rules. It’s great for building compilers, interpreters, or other tools that need to understand complex text formats.

  8. I am tasked with building a real-time simulation of vehicles in C++. What Boost libraries might give me the performance I need for real-time work, and support a simulation?

    Refer to Real-Time Simulation.

Licensing

  1. What is the license for Boost libraries?

    The Boost libraries are licensed under the Boost Software License, a permissive free software license that allows you to use, modify, and distribute the software under minimal restrictions. Refer to The Boost Software License.

Metaprogramming

  1. What is metaprogramming in the context of Boost C++?

    Metaprogramming is a technique of programming that involves generating and manipulating programs. In the context of Boost and C++, metaprogramming often refers to template metaprogramming, which uses templates to perform computations at compile-time.

  2. What is Boost.MP11?

    Boost.Mp11 is a Boost library designed for metaprogramming. It provides a set of templates and types for compile-time computations and manipulations, effectively extending the C++ template mechanism.

  3. What can I achieve with Boost.MP11?

    With Boost.Mp11, you can perform computations and logic at compile-time, thus reducing runtime overhead. For example, you can manipulate types, perform iterations, make decisions, and do other computations during the compilation phase.

  4. What is a typelist and how can I use it with Boost.MP11?

    A typelist is a compile-time container of types. It’s a fundamental concept in C++ template metaprogramming where operations are done at compile time rather than runtime, and types are manipulated in the same way that values are manipulated in regular programming.

    In the context of the Boost.Mp11 library, a typelist is a template class that takes a variadic list of type parameters. Here’s an example:

    #include <boost/mp11/list.hpp>

using my_typelist = boost::mp11::mp_list<int, float, double>;

    In this example, my_typelist is a typelist containing the types int, float, and double. Once you have a typelist, you can manipulate it using the metaprogramming functions provided by the library. For example:

    #include <boost/mp11/list.hpp>
#include <boost/mp11/algorithm.hpp>

using my_typelist = boost::mp11::mp_list<int, float, double>;

// Get the number of types in the list
constexpr std::size_t size = boost::mp11::mp_size<my_typelist>::value;

// Check if a type is in the list
constexpr bool contains_double = boost::mp11::mp_contains<my_typelist, double>::value;

// Add a type to the list
using extended_typelist = boost::mp11::mp_push_back<my_typelist, char>;

// Get the second type in the list
using second_type = boost::mp11::mp_at_c<my_typelist, 1>;

    In these examples, mp_size is used to get the number of types in the list, mp_contains checks if a type is in the list, mp_push_back adds a type to the list, and mp_at_c retrieves a type at a specific index in the list. All these operations are done at compile time.

  5. What are some limitations or challenges of metaprogramming with Boost.MP11?

    Metaprogramming with Boost.Mp11 can lead to complex and difficult-to-understand code, especially for programmers unfamiliar with the technique. Compile errors can be particularly cryptic due to the way templates are processed. Additionally, heavy use of templates can lead to longer compile times.

    Other challenges include lack of runtime flexibility, as decisions are made at compile time. And perhaps issues with portability can occur (say, between compilers) as metaprogramming pushes the boundaries of a computer language to its limits.

Boost.Mp11 supersedes the earlier Boost.Mpl and Boost.Preprocessor libraries.

Modular Boost

  1. What is meant by "Modular Boost"?

    Technically, Modular Boost consists of the Boost super-project and separate projects for each individual library in Boost. In terms of Git, the Boost super-project treats the individual libraries as submodules. Currently (early 2024) when the Boost libraries are downloaded and installed, the build organization does not match the modular arrangement of the Git super-project. This is largely a legacy issue, and there are advantages to the build layout matching the super-project layout. This concept, and the effort behind it, is known as "Modular Boost".

    Refer to the Super-project Layout topic (in the Contributor Guide) for a full description of the super-project.

  2. Will a Modular Boost affect the thrice-yearly Boost Release?

    No. The collection of libraries is still a single release, and there are no plans to change the release cadence.

  3. Will this require that the current Boost source structure is changed?

    Yes. Unfortunately there is one restriction that adhering to a modular Boost requires - there can be no sub-libraries. That is, we can’t support having libraries in the root/libs/<group name>/<library> format. All libraries must be single libraries under the root/libs directory. There’s only a handful of libraries that currently do not conform to this already (notably the root/libs/numeric/<name> group of libraries).

  4. Why do we want a Modular Boost?

    It’s easier on everyone if we adopt a flat hierarchy. The user will experience a consistent process no matter which libraries they want to use. Similarly for contributors, the creation process will be consistent. Also, tools can be written that can parse and analyze libraries without an awkward range of exceptions. This includes tools written by Boost contributors. For example, the tools that are used to determine library dependencies. And any tool that a user might want to write for their own, or shared, use.

    Other advantages of a modular format include:

    • Users of Boost can now choose to include only the specific modules they need for their project, rather than downloading and building the entire Boost framework. This can significantly reduce the size of the codebase and dependencies in a project, leading to faster compilation times and reduced resource usage.

    • Individual modules can be updated and released on their own schedule, independent of the rest of the libraries. This allows for quicker updates and bug fixes to individual libraries without waiting for a full release.

    • The structure aligns well with package managers like Conan, vcpkg, or Bazel, making it easier to manage Boost libraries within larger projects. Users can specify exactly which Boost libraries they need, and the package manager handles the inclusion and versioning.

  5. Will the proposed changes be backwards-compatible from the user’s perspective. In particular, the public header inclusion paths will still be <boost/numeric/<name>.hpp> rather than, say, <boost/numeric-conversion/<name>.hpp>, correct?

    Correct - backwards-compatibility should be maintained.

  6. When will Modular Boost be available to users?

    An exact timeline requires issues to be resolved, though later in 2024 is the current plan-of-record.

Releases

  1. How do I download the latest libraries?

    Go to Boost Downloads.

  2. What do the Boost version numbers mean?

    The scheme is x.y.z, where x is incremented only for massive changes, such as a reorganization of many libraries, y is incremented whenever a new library is added, and z is incremented for maintenance releases. y and z are reset to 0 if the value to the left changes

  3. Is there a formal relationship between Boost.org and the C++ Standards Committee?

    No, although there is a strong informal relationship in that many members of the committee participate in Boost, and the people who started Boost were all committee members.

  4. Will the Boost.org libraries become part of the next C++ Standard?

    Some might, but that is up to the standards committee. Committee members who also participate in Boost will definitely be proposing at least some Boost libraries for standardization. Libraries which are "existing practice" are most likely to be accepted by the C++ committee for future standardization. Having a library accepted by Boost is one way to establish existing practice.

  5. Is the Boost web site a commercial business?

    No. It is a non-profit.

  6. Why do Boost headers have a .hpp suffix rather than .h or none at all?

    File extensions communicate the "type" of the file, both to humans and to computer programs. The '.h' extension is used for C header files, and therefore communicates the wrong thing about C++ header files. Using no extension communicates nothing and forces inspection of file contents to determine type. Using .hpp unambiguously identifies it as C++ header file, and works well in practice.

  7. How do I contribute a library?

    Refer to the Contributor Guide. Note that shareware libraries, commercial libraries, or libraries requiring restrictive licensing are all not acceptable. Your library must be provided free, with full source code, and have an acceptable license. There are other ways of contributing too, providing feedback, testing, submitting suggestions for new features and bug fixes, for example. There are no fees for submitting a library.

Smart Pointers

  1. What different types of smart pointers are there?

    The Boost.SmartPtr library provides a set of smart pointers that helps in automatic and appropriate resource management. They are particularly useful for managing memory and provide a safer and more efficient way of handling dynamically allocated memory. The library provides the following types of smart pointers:

    • boost::scoped_ptr: A simple smart pointer for sole ownership of single objects that must be deleted. It’s neither copyable nor movable. Deletion occurs automatically when the scoped_ptr goes out of scope.

    • boost::scoped_array: Similar to scoped_ptr, but for arrays instead of single objects. Deletion occurs automatically when the scoped_array goes out of scope.

    • boost::shared_ptr: A reference-counted smart pointer for single objects or arrays, which automatically deletes the object when the reference count reaches zero. Multiple shared_ptr can point to the same object, and the object is deleted when the last shared_ptr referencing it is destroyed.

    • boost::shared_array: Similar to shared_ptr, but for arrays instead of single objects.

    • boost::weak_ptr: A companion to shared_ptr that holds a non-owning ("weak") reference to an object that is managed by shared_ptr. It must be converted to shared_ptr in order to access the referenced object.

    • boost::intrusive_ptr: A smart pointer that uses intrusive reference counting. Intrusive reference counting relies on the object to maintain the reference count, rather than the smart pointer. This can provide performance benefits in certain situations, but it requires additional support from the referenced objects.

    • boost::enable_shared_from_this: Provides member function shared_from_this, which enables an object that’s already managed by a shared_ptr to safely generate more shared_ptr instances that all share ownership of the same object.

    • boost::unique_ptr: A smart pointer that retains exclusive ownership of an object through a pointer. It’s similar to std::unique_ptr in the C++ Standard Library.

  2. Can you give me a brief coding overview of how to use smart pointers efficiently?

    There are several types of smart pointers with different characteristics and use cases, so use them appropriately according to your program’s requirements. Here are some common examples:

    A shared_ptr is a reference-counting smart pointer, meaning it retains shared ownership of an object through a pointer. When the last shared_ptr to an object is destroyed, the pointed-to object is automatically deleted. For example:

    #include <boost/shared_ptr.hpp>

void foo() {
    boost::shared_ptr<int> sp(new int(10));
    // Now 'sp' owns the 'int'.
    // When 'sp' is destroyed, the 'int' will be deleted.
}

    Note that shared_ptr objects can be copied, meaning ownership of the memory can be shared among multiple pointers. The memory will be freed when the last remaining shared_ptr is destroyed. For example:

    #include <boost/shared_ptr.hpp>

void foo() {
    boost::shared_ptr<int> sp1(new int(10));
    // Now 'sp1' owns the 'int'.
    boost::shared_ptr<int> sp2 = sp1;
    // Now 'sp1' and 'sp2' both own the same 'int'.
    // The 'int' will not be deleted until both 'sp1' and 'sp2' are destroyed.
}

    A weak_ptr is a smart pointer that holds a non-owning ("weak") reference to an object managed by a shared_ptr. It must be converted to shared_ptr in order to access the object. For example:

    #include <boost/shared_ptr.hpp>
#include <boost/weak_ptr.hpp>

void foo() {
    boost::shared_ptr<int> sp(new int(10));
    boost::weak_ptr<int> wp = sp;
    // 'wp' is a weak pointer to the 'int'.
    // If 'sp' is destroyed, 'wp' will be able to detect it.
}

    A unique_ptr is a smart pointer that retains exclusive ownership of an object through a pointer. It’s similar to std::unique_ptr in the C++ Standard Library. For example:

    #include <boost/interprocess/smart_ptr/unique_ptr.hpp>

void foo() {
    boost::movelib::unique_ptr<int> up(new int(10));
    // Now 'up' owns the 'int'.
    // When 'up' is destroyed, the 'int' will be deleted.
}

Templates

  1. What are C++ templates?

    C++ templates are a powerful feature of the language that allows for generic programming. They enable the creation of functions or classes that can operate on different data types without having to duplicate code.

  2. What are function templates in C++?

    Function templates are functions that can be used with any data type. You define them using the keyword template followed by the template parameters. Function templates allow you to create a single function that can operate on different data types.

  3. What is template specialization in C++?

    Template specialization is a feature of C++ templates that allows you to define a different implementation of a template for a specific type or set of types. It can be used with both class and function templates.

  4. What are the benefits and drawbacks of using templates in C++?

    The benefits of using templates include code reusability, type safety, and the ability to use generic programming paradigms. The drawbacks include potentially increased compile times, difficult-to-understand error messages, and complexities associated with template metaprogramming.

  5. How can I use templates to implement a generic sort function in C++?

    Here’s a simple example of how you might use a function template to implement a generic sort function:

    template <typename T>
void sort(T* array, int size) {
    for(int i = 0; i < size; i++) {
        for(int j = i + 1; j < size; j++) {
            if(array[i] > array[j]) {
                T temp = array[i];
                array[i] = array[j];
                array[j] = temp;
            }
        }
    }
}

    This function can now be used to sort arrays of any type (that supports the < and > operators), not just a specific type.

See Also