Syntax and rule analysis of C++ variable parameters

C Variable parameters allow the function to accept any number of parameters. The syntax is: returnType functionName(type1 arg1, ..., typeN argN, ...). The rules include: it must be placed after the fixed parameter, there can only be one, the type must be a built-in type, a class object or a pointer, and the quantity is determined when calling. In practice, the sum function calculates the sum of all parameters: int sum(int n, ...) {...}.

C Syntax and rule analysis of variable parameters

Variable parameters are a special function parameter syntax in C, which allows the function to accept any number parameters. This is useful when implementing functions that need to adapt to dynamically changing parameter lists.

Syntax

returnType functionName(type1 arg1, type2 arg2, ..., typeN argN, ...)

Where:

• returnType is the return value type of the function.
• functionName is the name of the function.
• arg1, arg2, ..., argN are of types type1, type2# respectively Fixed parameters of ##, ..., typeN.
• ... represents variable parameters. The ellipsis can be followed by an identifier that indicates the type of the variadic argument.

Rules

The rules for variable parameters are as follows:

Variable parameters must be placed after fixed parameters.
• There can only be one variable parameter.
• The type of variable parameters must be a built-in type, class object or pointer type.
• The number of variable parameters can only be determined when calling.

Practical case

In the following example, we define a variable parameter function

sum to calculate the sum of all its parameters:

int sum(int n, ...)
{
    va_list args;
    va_start(args, n);

    int result = n;
    int arg;
    while ((arg = va_arg(args, int)) != 0)
    {
        result += arg;
    }

    va_end(args);
    return result;
}

Now we can call this function like this, passing any number of arguments:

int total1 = sum(1, 2, 3, 4, 5); // 总和为 15
int total2 = sum(2, 4, 6, 8, 10); // 总和为 30

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