C++翻译阶段的混乱
有人可以解释为什么以下不起作用吗？
int main() // Tried on several recent C++ '03 compilers.
{
#define FOO L
const wchar_t* const foo = FOO"bar"; // Will error out with something like: "identifier 'L' is undefined."
#undef FOO
}
我认为预处理是在比字符串文字操作和一般标记翻译更早的翻译阶段完成的。
编译器不会或多或少地看到这一点：
int main()
{
const wchar_t* const foo = L"bar";
}
如果有人可以引用标准中的解释，那就太好了。
Can someone explain why the following doesn't work?
int main() // Tried on several recent C++ '03 compilers.
{
#define FOO L
const wchar_t* const foo = FOO"bar"; // Will error out with something like: "identifier 'L' is undefined."
#undef FOO
}
I thought that preprocessing was done in an earlier translation phase than string literal operations and general token translation.
Wouldn't the compiler be more or less seeing this:
int main()
{
const wchar_t* const foo = L"bar";
}
It would be great if someone could cite an explanation from the standard.
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使用：
如果没有尾随
\，则L和宏替换的字符串之间将有一个空格。这是来自g++ -E的结果：Use:
without the trailing
\there will be a space betweenLand the string on macro substitution. This is from the result ofg++ -E:作为约翰答案的替代方案，我认为您可以按照 Microsoft 的 _T() 定义方式来定义它：
并像这样使用它：
这会将 L 与文本适当地连接起来。
As an alternative to John's answer, I think you could define this the way Microsoft's _T() is defined:
and use it like this:
This will concatenate the L with the text appropriately.
您收到的错误消息意味着它在执行其他操作之前正在预处理您的
#define，它只是不知道它最终的含义是什么（在替换所有FOO之后） >s 与Ls，它会查找L的含义，但无法弄清楚）。编译器正在查看您的第二段代码，它只是不知道此时
L"bar"的含义。您确定所有内容都已正确定义并包含吗？
The error message you're getting means that it is preprocessing your
#definebefore it does anything else, it just doesn't know what it ends up meaning (after replacing allFOOs withLs, it looks for whatLmeans and can't figure it out).The compiler is seeing your second bit of code, it just doesn't know what
L"bar"means at that point.Are you sure everything is defined and included properly?
查看预处理器的输出 (g++ -E)
L 后面有一个空格。
Look at the output from the preprocessor (g++ -E)
There's a space after your L.