在C / C参数可变型函数和参数分配++ [英] Variadic functions and arguments assignment in C/C++

问题描述

我在想，如果在C / C ++语言，可以传递参数以键值的形式运作。
例如，在Python中，你可以这样做：

I was wondering if in C/C++ language it is possible to pass arguments to function in key-value form. For example in python you can do:

def some_function(arg0 = "default_value", arg1):
    # (...)

value1 = "passed_value"
some_function(arg1 = value1)

那么在C替代code可能是这样的：

So the alternative code in C could look like this:

void some_function(char *arg0 = "default_value", char *arg1)
{
    ;
}

int main()
{
    char *value1 = "passed_value";
    some_function(arg1 = value1);
    return(0);
}

因此​​，参数在some_function使用将是：

So the arguments to use in some_function would be:

为arg0 =DEFAULT_VALUE

arg0 = "default_value"

ARG1 =passed_value

arg1 = "passed_value"

任何想法？

推荐答案

下面是一个C99的解决方案使用复合文字和复杂的宏：

Here's a C99 solution using compound literals and variadic macros:

#include <stdio.h>

#define some_func(...) some_func_((struct some_func_args_){ __VA_ARGS__ })

struct some_func_args_
{
    const char *arg1;
    const char *arg2;
};

static void some_func_(struct some_func_args_ args)
{
    if(!args.arg1) args.arg1 = "default";
    printf("---\narg1 = %s\narg2 = %s\n", args.arg1, args.arg2);
}

int main(void)
{
    some_func("foo", "bar");
    some_func(.arg1 = "spam");
    some_func(.arg2 = "eggs");
    return 0;
}

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