çpreprocessor字面解释 [英] C preprocessor Literal Construction

问题描述

我的问题是：

我有一个字符串文字是宏观ED像这样

I have a string literal that is macro-ed like so

#define TITLE "Title"

但也有这样的情况，我需要在此字符串的一个宽字符变种通过。我希望能够通过 L标题这些功能。所以很自然，我开始尝试在标题的角度来定义一个新宏 W_TITLE 。

But there are instances when I need to pass in a wide char variant of this string. I want to be able to pass L"Title" to those functions. So naturally, I set out trying to define a new macro W_TITLE in terms of TITLE.

但我有没有运气，我所有的方法（下面进行说明）都失败了。请告诉我这种法宝怎么得来的。

But I have no luck, all my approaches (listed bellow) have failed. Please tell me how such magic can be accomplished.

我试过

#define W_TITLE L##TITLE
#define W_TITLE #L TITLE
#define W_TITLE ##L TITLE

但他们都失败...

But they all fail...

推荐答案

试试这个：

#define WIDEN_(exp)   L##exp
#define WIDEN(exp)    WIDEN_(exp)
#define TITLE         "Title"
#define W_TITLE       WIDEN(TITLE)

您需要强制的扩展，通过一个中间的宏让你在找什么。

You need to force an expansion through an intermediate macro to get what you're looking for.

#include <stdio.h>

#define WIDEN_(exp)   L##exp
#define WIDEN(exp)    WIDEN_(exp)
#define TITLE         "Title"
#define W_TITLE       WIDEN(TITLE)

int main(int argc, char *argv[])
{
    printf("%s\n", TITLE);
    wprintf(L"%ls\n", W_TITLE);
    return 0;
}

结果：

Title
Title

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