Can You Concatenate Two String Literals Directly in C ?

Concatenating String Literals

In C , you can concatenate strings using the operator. However, there are certain rules to follow when concatenating string literals.

Validity of String Definitions

The following code defines two string variables:

<code class="cpp">const string hello = "Hello";
const string message = hello + ",world" + "!";</code>

This code is valid because one of the two strings being concatenated is a std::string object (hello). The operator will evaluate the concatenation of hello and ",world" first, resulting in a std::string object. This object is then concatenated with "!".

However, the following code is invalid:

<code class="cpp">const string exclam = "!";
const string message = "Hello" + ",world" + exclam;</code>

This code is invalid because both strings being concatenated in the leftmost are string literals ("Hello" and ",world"). The operator cannot be used to concatenate two string literals directly.

Left-to-Right Associativity of Operator

The operator in C has left-to-right associativity. This means that the equivalent parenthesized expression for the second example code is:

<code class="cpp">const string message = (("Hello" + ",world") + exclam);</code>

As you can see, the two string literals "Hello" and ",world" are concatenated first, resulting in a compile-time error.

Overcoming the Limitation

There are several ways to overcome this limitation:

1. Use a std::string Object:

<code class="cpp">const string message = string("Hello") + ",world" + exclam;</code>

2. Parenthesize the Expression:

<code class="cpp">const string message = "Hello" + (",world" + exclam);</code>

Reason for the Limitation

The limitation of not being able to concatenate two string literals directly is because a string literal is an array of characters (a const char [N] where N 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.

Therefore, when you try to concatenate two string literals using , you are effectively trying to add two const char* pointers together. This is not possible because adding two pointers does not make sense in the context of string concatenation.

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