How Can I Directly Concatenate String Literals in C/C Macros?

String Concatenation in C/C Macros

When defining macros with string literals, it's often necessary to concatenate them to form a new string. Let's consider an example:

#define STR1      "s"
#define STR2      "1"
#define STR3      STR1 ## STR2

The question arises: is it possible to directly concatenate STR1 and STR2 to obtain "s1" using a single macro definition?

Standard String Concatenation

Traditionally, string concatenation in macros is achieved by utilizing the stringification operator (#). However, this approach entails passing arguments to an intermediate macro function.

#define CONCAT(x, y) x ## y
#define STR3 CONCAT(STR1, STR2)

Simplified Concatenation for Strings

For the specific case of concatenating string literals, a simplified approach exists. By omitting the stringification operator, we can directly concatenate the strings:

#define STR3 STR1 STR2

This expands to:

#define STR3 "s" "1"

In the C language, juxtaposing strings with spaces (as in "s" "1") is equivalent to having a single string "s1". Therefore, this simplified method provides a direct way to concatenate string literals in C/C macros.

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