


Why are Default Template Arguments Restricted to Class Templates in C ?
Nov 01, 2024 pm 05:29 PMWhy Default Template Arguments are Restricted to Class Templates
In C , default template arguments are only allowed on class templates but not on function templates. This restriction may seem surprising, but there are several reasons behind it.
Default Template Arguments for Class Templates
Default template arguments allow class templates to provide a default value for certain parameters. This can be useful when the default value is unlikely to change for most instances of the template. For example, a class template for a sorting algorithm could have a default template argument for the comparison function used in sorting.
Restriction for Function Templates
However, default template arguments are not allowed for function templates because they would introduce ambiguity. Consider the following hypothetical example:
<code class="cpp">struct my_class { template<class T = int> void mymember(T* vec) { // ... } };</code>
In this example, it would be unclear whether T is the default type for the mymember function or for the my_class template itself. This ambiguity could lead to subtle errors in the code.
Advent of C 11
Prior to C 11, the prohibition of default template arguments for function templates was a significant limitation. However, C 11 introduced a new feature called "type aliases" which allows us to define aliases for types. This provides a workaround for the lack of default template arguments for function templates. For example, the example above could be rewritten as follows:
<code class="cpp">struct my_class { typedef int default_type; template<class T = default_type> void mymember(T* vec) { // ... } };</code>
While type aliases are not as convenient as default template arguments, they provide a similar functionality and allow us to overcome the limitations of the current C standard.
Bjarne Stroustrup's Perspective
In a defect report, Bjarne Stroustrup, the original designer of C , expressed his view on the prohibition of default template arguments for function templates:
The prohibition of default template arguments for function templates is a misbegotten remnant of the time where freestanding functions were treated as second class citizens and required all template arguments to be deduced from the function arguments rather than specified.
The above is the detailed content of Why are Default Template Arguments Restricted to Class Templates in C ?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

Yes, function overloading is a polymorphic form in C, specifically compile-time polymorphism. 1. Function overload allows multiple functions with the same name but different parameter lists. 2. The compiler decides which function to call at compile time based on the provided parameters. 3. Unlike runtime polymorphism, function overloading has no extra overhead at runtime, and is simple to implement but less flexible.

C has two main polymorphic types: compile-time polymorphism and run-time polymorphism. 1. Compilation-time polymorphism is implemented through function overloading and templates, providing high efficiency but may lead to code bloating. 2. Runtime polymorphism is implemented through virtual functions and inheritance, providing flexibility but performance overhead.

Yes, polymorphisms in C are very useful. 1) It provides flexibility to allow easy addition of new types; 2) promotes code reuse and reduces duplication; 3) simplifies maintenance, making the code easier to expand and adapt to changes. Despite performance and memory management challenges, its advantages are particularly significant in complex systems.

C destructorscanleadtoseveralcommonerrors.Toavoidthem:1)Preventdoubledeletionbysettingpointerstonullptrorusingsmartpointers.2)Handleexceptionsindestructorsbycatchingandloggingthem.3)Usevirtualdestructorsinbaseclassesforproperpolymorphicdestruction.4

Polymorphisms in C are divided into runtime polymorphisms and compile-time polymorphisms. 1. Runtime polymorphism is implemented through virtual functions, allowing the correct method to be called dynamically at runtime. 2. Compilation-time polymorphism is implemented through function overloading and templates, providing higher performance and flexibility.

People who study Python transfer to C The most direct confusion is: Why can't you write like Python? Because C, although the syntax is more complex, provides underlying control capabilities and performance advantages. 1. In terms of syntax structure, C uses curly braces {} instead of indentation to organize code blocks, and variable types must be explicitly declared; 2. In terms of type system and memory management, C does not have an automatic garbage collection mechanism, and needs to manually manage memory and pay attention to releasing resources. RAII technology can assist resource management; 3. In functions and class definitions, C needs to explicitly access modifiers, constructors and destructors, and supports advanced functions such as operator overloading; 4. In terms of standard libraries, STL provides powerful containers and algorithms, but needs to adapt to generic programming ideas; 5

C polymorphismincludescompile-time,runtime,andtemplatepolymorphism.1)Compile-timepolymorphismusesfunctionandoperatoroverloadingforefficiency.2)Runtimepolymorphismemploysvirtualfunctionsforflexibility.3)Templatepolymorphismenablesgenericprogrammingfo

C polymorphismisuniqueduetoitscombinationofcompile-timeandruntimepolymorphism,allowingforbothefficiencyandflexibility.Toharnessitspowerstylishly:1)Usesmartpointerslikestd::unique_ptrformemorymanagement,2)Ensurebaseclasseshavevirtualdestructors,3)Emp
