c++ - 递增引用变量不起作用

<分区>

下面的代码应该输出 6，但它却输出 5。我不知道为什么。怎么回事？

#include <iostream>

template <typename T>
void foo(T& y)
{
   y++;
}

int main()
{
   int x = 5;

   // Why won't this line work???/
   foo(x);

   std::cout << x;
}

Live demo

最佳答案

三字母表

您正在使用 trigraphs 的好技巧.

// Why won't this line work???/
                            | |
                            \ /
                             |
                         ~trigraph~

??/ 三字母依次转换为 \，它基本上将当前行与下一行连接起来，因此您的代码或多或少会变成这样:

// Why won't this line work? foo(x);

确实是个绝招。

引用自 C++11 标准:

§2.2.2:

Each instance of a backslash character (\) immediately followed by a new-line character is deleted, splicing physical source lines to form logical source lines. ...

§2.4.1:

Table 1 - Trigraph sequences
...
==========================
| Trigraph | Replacement |
==========================
|          ...           |
==========================
|   ??/    |      \      |
==========================

幸运的是，GCC seems to detect this kind of trickery ，发出警告(只需设置 -Wall):

main.cpp:13:32: warning: trigraph ??/ converted to \ [-Wtrigraphs]
    // Why won't this line work???/
 ^

main.cpp:13:4: warning: multi-line comment [-Wcomment]
    // Why won't this line work???/
    ^

<子> 相关引用:

meaning of `???-` in C++ code

What is this smiley-with-beard expression: "<:]{%>"?

What does the C ??!??! operator do?

还有所有其他类似的问题。 ??)

_{PS:那是笑脸。}

关于c++ - 递增引用变量不起作用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/17442912/