连接两个字符串文字(Concatenate two string literals)

 我非常新的编程，并且正在阅读Koenig的Accelerated C ++。 无论如何，我正在学习字符串，他写道：“新的想法是，我们可以使用+来连接一个字符串和一个字符串文字，或者说，就是两个字符串（但不是两个字符串文字）。 
 
 好的，这是有道理的。 现在进行两个单独的练习，旨在照亮这一点。 
 
 以下定义是否有效？ 
 
const string hello = "Hello";

const string message = hello + ",world" + "!";
 
 现在，我试图执行上面的工作！ 所以我很高兴 
 
 然后我试着做下一个练习; 
 
const string exclam = "!";

const string message = "Hello" + ",world" + exclam;
 
 这没有办法。 现在我明白这与事实上有关，你不能连接两个字符串文字，但我不明白为什么我设法得到第一个例子工作之间的语义差异（不是“，世界”和“！ “两个字符串文字？这不是没有工作吗？）但不是第二个。 
 
 谢谢！ 

I am reading Accelerated C++ by Koenig. He writes that "the new idea is that we can use + to concatenate a string and a string literal - or, for that matter, two strings (but not two string literals).
 
Fine, this makes sense I suppose. Now onto two separate exercises meant to illuminate this . 
 
Are the following definitions valid?
 
const string hello = "Hello";

const string message = hello + ",world" + "!";
 
Now, I tried to execute the above and it worked! So I was happy.
 
Then I tried to do the next exercise; 
 
const string exclam = "!";

const string message = "Hello" + ",world" + exclam;
 
This did not work. Now I understand it has something to do with the fact that you cannot concatenate two string literals, but I don't understand the semantic difference between why I managed to get the first example to work (isn't ",world" and "!" two string literals? Shouldn't this not have worked?) but not the second.

原文：https://stackoverflow.com/questions/6061648