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    <pre><code>const string message = "Hello" + ",world" + exclam; </code></pre> <p>The <code>+</code> operator has left-to-right associativity, so the equivalent parenthesized expression is:</p> <pre><code>const string message = (("Hello" + ",world") + exclam); </code></pre> <p>As you can see, the two string literals <code>"Hello"</code> and <code>",world"</code> are "added" first, hence the error.</p> <p>One of the first two strings being concatenated must be a <code>std::string</code> object:</p> <pre><code>const string message = string("Hello") + ",world" + exclam; </code></pre> <p>Alternatively, you can force the second <code>+</code> to be evaluated first by parenthesizing that part of the expression:</p> <pre><code>const string message = "Hello" + (",world" + exclam); </code></pre> <p>It makes sense that your first example (<code>hello + ",world" + "!"</code>) works because the <code>std::string</code> (<code>hello</code>) is one of the arguments to the leftmost <code>+</code>. That <code>+</code> is evaluated, the result is a <code>std::string</code> object with the concatenated string, and that resulting <code>std::string</code> is then concatenated with the <code>"!"</code>.</p> <hr> <p>As for <em>why</em> you can't concatenate two string literals using <code>+</code>, it is because a string literal is just an array of characters (a <code>const char [N]</code> where <code>N</code> is the length of the string plus one, for the null terminator). When you use an array in most contexts, it is converted into a pointer to its initial element. </p> <p>So, when you try to do <code>"Hello" + ",world"</code>, what you're really trying to do is add two <code>const char*</code>s together, which isn't possible (what would it mean to add two pointers together?) and if it was it wouldn't do what you wanted it to do. </p> <hr> <p>Note that you <em>can</em> concatenate string literals by placing them next to each other; for example, the following two are equivalent:</p> <pre><code>"Hello" ",world" "Hello,world" </code></pre> <p>This is useful if you have a long string literal that you want to break up onto multiple lines. They have to be string literals, though: this won't work with <code>const char*</code> pointers or <code>const char[N]</code> arrays.</p>
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    1. POConcatenate two string literals
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    1. USJames McNellis
    1. USJames McNellis
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    1. POConcatenate two string literals
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    1. COAlso, `const string message = "Hello" + (",world"+exclam);` will work too, because of explicit parenthesization (is that a word?).
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      1. USChinmay Kanchi
    2. COCould be even more complete if you point out why the first example works: `const string message = ((hello + ",world") + "!");`
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      1. USMark Ransom
    3. COThank you! I suspected it had something to do with left-to-right associativity but wasn't sure and this semantic difference didn't make much sense to me. I appreciate the answer!
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      1. USArthur Collé
 

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