C++ function variable parameter passing mechanism

C The variable parameter passing mechanism allows the function to accept an indefinite number of parameters. The syntax is to use the ... ellipse symbol to indicate variable parameters. Common applications include formatted output, such as the printf() function, which uses va_list to access a variadic argument list.

C function variable parameter passing mechanism

Introduction

C provides The variadic parameter passing mechanism allows functions to accept an indeterminate number of parameters. This is useful in scenarios where you need to process data from different sources or dynamically create parameter lists.

Syntax

A variadic function is a function that declares formal parameters with ... omitted symbols. The ellipsis indicates that the function can accept an indefinite number of arguments of this type.

For example:

void printArgs(const char* fmt, ...)
{
    // ... 代码
}

Practical case: formatted output

A common application of the variable parameter passing mechanism is formatted output. The following code demonstrates how to use the printf() function to output a variable number of parameters:

#include <iostream>
#include <stdarg.h>

using namespace std;

void print(const char* fmt, ...)
{
    va_list args;
    va_start(args, fmt);
    vprintf(fmt, args);
    va_end(args);
}

int main()
{
    print("Hello, %s!", "world");
    print("Average: %d, %d, %d", 1, 2, 3);

    return 0;
}

Output:

Hello, world!
Average: 1, 2, 3

Access Parameters

You can use va_list to access parameters in the variable parameter list. va_start() initializes the va_list object, and va_arg() is used to get the next argument.

See the C standard library documentation for more details on va_list and va_arg().

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