Default argument

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In computer programming, a default argument is an argument to a function that a programmer is not required to specify. In most programming languages, functions may take one or more arguments. Usually, each argument must be specified in full (this is the case in the C programming language).

Later languages (for example, in C++) allow the programmer to specify default arguments that always have a value, even if one is not specified when calling the function. For example, in the following function definition:

int MyFunc(int a, int b, int c=12);

This function takes three arguments, of which the last one has a default of twelve. The programmer may call this function in two ways:

result = MyFunc(1, 2, 3);

result = MyFunc(1, 2);

In the first case the value for the argument called c is specified as normal. In the second one, the argument is omitted, and the default value of 12 will be used instead.

There's no means to know if the argument has been specified by the caller or if the default value was used.