How Can I Concatenate Macro-Defined Strings in C/C Without the Operator?

Macro-Based String Concatenation in C/C

Directly concatenating macro-defined strings in C/C is not possible using the ## preprocessor operator, which is primarily intended for token concatenation. However, a workaround exists to achieve this.

Consider the following example:

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

This code defines three macros: STR1 with the string literal "s", STR2 with "1", and STR3 as the concatenation of STR1 and STR2. The expansion of STR3 results in:

#define STR3 "s" "1"

However, in the C language, the juxtaposition of two strings separated by whitespace (as in "s" "1") is equivalent to a single string "s1".

Therefore, the following code directly concatenates STR1 and STR2 without the need for the ## operator:

#define STR3 STR1 STR2

This expands to:

#define STR3 "s1"

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