Functions with Variable Number of Arguments in C++

Introduction to Variable Arguments

In C++ programming, you can find yourself in a scenario where you need a function that can take a variable number of arguments, i.e., parameters, rather than a fixed number. The C/C++ programming language has a solution for this problem; you can construct a function that accepts various parameters depending on your needs.

Based on user requirements, a variable number of arguments can be of two types:

• When the data type of all the arguments is the same
• When the data type of all the arguments is different.

Implementation Technique of Variable Arguments before C++11 Update

When the Data Type of all the Arguments Is the Same

In this case, a vector or an array of the required data type can be passed in a function.

Syntax:

When the Data Type of all the Arguments is Different.

In this case, variadic functions are declared under the cstdarg header file.

Implementation Technique of Variable Arguments after C++11 Update

When the Data Type of all the Arguments is the Same

After the C++11 update, we have the concept of an initializer list that can take the same data type variable arguments. For this, the header file <intializer_list> needs to be included.

Syntax:

When the Data Type of all the Arguments is Different.

Variadic templates can also be used to generate functions with variable arguments. Variadic templates have the advantage of not imposing limits on the types of arguments, not performing integral and floating-point promotions, and being type-safe.

Steps To Implement the Functionality of Variable Arguments

In this section, we will see some examples of functions with a variable number of arguments in C++.

Implementation of Same Data Type Variable Arguments

Implementation Using "vector":

• Include <vector> header file.
• Define a function having parameter as a vector of required data type.
• Call the above-defined function from the main() function with parameter as the variable arguments inside the curly braces.

Code:

Output:

Implementation Using "initializer_list":

• Include <initializer_list> header file.
• Define a function having a parameter as an initializer_list of the required data type.
• Call the above-defined function from the main() function with parameter as the variable arguments inside the curly braces.

Code:

Output:

Implementation of Different Data Type Variable Arguments

Implementation Using "cstdarg"

The header file cstdarg contains variadic functions and macros for implementing a function's variable number of arguments.

Variadic functions take a variable number of arguments (for example, std::printf). An ellipsis appears after the list of parameters, e.g., int printf(const char* format...);, which may be preceded by an optional comma, to declare a variadic function.

The following library facilities are given to access the variadic arguments from the function body:

Code

Output:

Implementation Using Variadic Templates

• Declare a template with typename T.
• Define a function with a parameter t of datatype T.
• Declare another template with typename T and typename... Args.
• Define another function with the same name having two parameters. First, t with datatype T, and the second, args with type Args....
• Call the above function from the main() function with variable number of arguments.

Code:

Output:

Examples of Functions with Variable Number of Arguments In C++

Finding Maximum of Integer and Floating Point Numbers

Code:

Output:

See Also:

• Header files in C++