C ++中函数中可变数量的参数

2021-12-29 00:00:00 c syntax c++ variadic-functions

如何在我的 C++ 函数中使用可变数量的参数.

How I can have variable number of parameters in my function in C++.

C# 中的模拟:

public void Foo(params int[] a) {
    for (int i = 0; i < a.Length; i++)
        Console.WriteLine(a[i]);
}

public void UseFoo() {
    Foo();
    Foo(1);
    Foo(1, 2);
}

Java 中的模拟:

public void Foo(int... a) {
    for (int i = 0; i < a.length; i++)
        System.out.println(a[i]);
}

public void UseFoo() {
    Foo();
    Foo(1);
    Foo(2);
}

推荐答案

这些被称为 Variadic 函数.维基百科列出了C++ 示例代码.

These are called Variadic functions. Wikipedia lists example code for C++.

可移植地实现可变参数C编程中的函数语言，标准的 stdarg.h 标头应该使用文件.年长的varargs.h 标头已被弃用赞成 std??arg.h.在 C++ 中，应使用头文件 cstdarg.

To portably implement variadic functions in the C programming language, the standard stdarg.h header file should be used. The older varargs.h header has been deprecated in favor of stdarg.h. In C++, the header file cstdarg should be used.

要创建一个可变参数函数，一个省略号 (...) 必须放在参数列表的结尾.在 - 的里面函数体，一个变量必须定义类型 va_list.那么宏 va_start(va_list, last fixedparam), va_arg(va_list, cast type),va_end(va_list) 可以使用.为了例子:

To create a variadic function, an ellipsis (...) must be placed at the end of a parameter list. Inside the body of the function, a variable of type va_list must be defined. Then the macros va_start(va_list, last fixed param), va_arg(va_list, cast type), va_end(va_list) can be used. For example:

#include <stdarg.h>

double average(int count, ...)
{
    va_list ap;
    int j;
    double tot = 0;
    va_start(ap, count); //Requires the last fixed parameter (to get the address)
    for(j=0; j<count; j++)
        tot+=va_arg(ap, double); //Requires the type to cast to. Increments ap to the next argument.
    va_end(ap);
    return tot/count;
}

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