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Introduction

In this article we are going to discuss about the C++11 vs C++14 which is the common topic in the C++ interview question. Lets dive deep in the ocean of the difference of C++11 and C++14. C++11, was introduced in 2011, marked a significant overhaul of the C++ language, which is bringing in the numerous features whose aim is to improve coding efficiency, performance, and simplicity

C++14was introduced three years later in 2014, was a more incremental update aimed at refining the innovations brought by C++11. While C++11 laid the groundwork for modern C++, C++14 made subtle but impactful refinements which help to enhanced developer productivity and language flexibility.

Summary of Key Differences​

FeatureC++11C++14
constexprLimited to trivial functionsRelaxed rules, supports complex logic
Variable TemplatesNot availableIntroduced variable templates
Lambda ExpressionsExplicit parameter typesGeneric lambdas with auto parameters
Auto Return Type DeductionRequires explicit return typeAutomatic deduction of return types
std::make_uniqueNot availableIntroduced for safer dynamic memory usage
New AlgorithmsBasic algorithmsAdditional algorithms with lambda support

1. Improvements and Fixes in C++14​

C++11 was a major release that changed how C++ programs were written, while C++14 was a relatively minor update but with useful refinements. Some of the changes in C++14 focused on enhancing the new features in C++11 by fixing issues and improving usability.

1.1 Relaxed constexpr​

In C++11, constexpr was quite restrictive. It could only contain a single return statement or trivial operations. C++14 relaxed these constraints, allowing for more complex expressions and loops in constexpr functions, making constexpr much more powerful and enabling compile-time computation in cases previously not possible.

1.2 Variable Templates​

C++14 introduced variable templates, allowing the definition of templated variables, particularly useful for defining constants. In C++11, constexpr functions or static members were used for this purpose, but variable templates provide a more concise syntax.

1.3 Generic Lambdas​

C++11 introduced lambda functions as a powerful way to define anonymous functions in code. C++14 enhanced these with generic lambdas, allowing template-like behavior within lambdas by using auto for parameter types, eliminating the need to explicitly specify them.

2. Differences in Language Features​

2.1 Lambda Expressions and Generic Lambdas​

In C++11, lambda expressions were introduced to define anonymous functions directly within code, but parameter types had to be explicitly declared. C++14 introduced generic lambdas, allowing the use of auto for parameters, making lambdas more flexible and template-like.

Example:

  • C++11:
    auto lambda = [](int x, int y) { return x + y; };
  • C++14:
    auto lambda = [](auto x, auto y) { return x + y; };

2.2 constexpr Enhancements​

The restrictions on constexpr functions in C++11 allowed only a single return statement or simple operations. C++14 relaxed these to include more complex logic, such as loops and multiple statements.

Example:

  • C++11:
    constexpr int square(int x) { return x * x; }
  • C++14:
    constexpr int factorial(int n) {
        int result = 1;
        for (int i = 1; i <= n; ++i)
            result *= i;
        return result;
    }

2.3 Auto Return Type Deduction​

In C++11, auto simplified variable declaration but required explicit return types in functions. C++14 introduced automatic return type deduction for functions, making code cleaner and reducing redundancy.

Example:

  • C++11:
    auto add(int x, int y) -> int { return x + y; }
  • C++14:
    auto add(int x, int y) { return x + y; }

3. Performance and Optimizations​

Both C++11 and C++14 were designed with performance in mind, but C++14 introduced further optimization and allowed for more concise code, contributing to performance improvements.

3.1 Compile-Time computation​

With relaxed constexpr rules, more computations can be performed at compile time in C++14, leading to faster runtime execution. This is especially useful in high-performance applications, such as game development or high-frequency trading.

3.2 Improved Compiler Optimizations​

The enhancements in C++14, such as better handling of lambdas and constexpr functions, provide more opportunities for compiler optimizations, reducing runtime overhead.

Notable Optimizations and Enhancements:​

  • Relaxed constexpr: Allows complex expressions like loops and conditional statements at compile time, reducing runtime overhead.
  • Generalized Lambda Captures (init-captures): Lambdas can initialize variables directly in the capture list, reducing code complexity and improving performance.
  • Automatic Return Type Deduction: Improves inlining and optimizations by allowing the compiler to automatically deduce return types.
  • Binary Literals and Digit Separators: Improves readability of large constants, sometimes aiding optimization when working directly with hardware.
  • Enhanced STL Optimizations: C++14 optimized STL algorithms and data structures, leveraging move semantics and reducing redundant memory allocations.

4. Standard Library Additions​

4.1 std::make_unique​

C++14 introduced std::make_unique, a safer and more convenient way to create objects managed by std::unique_ptr, following the example of std::make_shared from C++11.

Example:

  • C++11:
    std::unique_ptr<int> ptr(new int(5));
  • C++14:
    auto ptr = std::make_unique<int>(5);

std::integer_sequence facilitates operations like unpacking arguments in a type-safe manner, improving template metaprogramming efficiency.

4.3 New Algorithms​

C++14 added new algorithms like std::equal with support for function objects and lambdas, along with updates to std::mismatch and std::is_permutation.

5. Deprecations and Fixes​

5.1 Removal of Deprecated Features​

C++14 deprecated certain features from C++98 in favor of modern alternatives, ensuring the language remains modern and aligned with best practices.

6. Impact on Codebase and Development​

6.1 Transition from C++11 to C++14​

The transition from C++11 to C++14 is mostly backward-compatible. However, new C++14 features can simplify code and enhance maintainability.

6.2 Writing More Concise Code​

With features like auto return type deduction and variable templates, C++14 enables more concise and readable code, reducing boilerplate and enhancing maintainability.

6.3 Compile-Time Improvements​

Relaxed constraints on constexpr allow more computations at compile-time, benefiting performance where execution speed is critical.

Conclusion

The differences between C++11 and C++14 are evolutionary rather than revolutionary. C++11 redefined the language, while C++14 refined and polished that vision, making C++ more powerful, flexible, and easier to use. Developers will benefit from C++14’s increased performance, cleaner syntax, and tools for handling complex problems more effectively.

Reference​