Token pasting
suggest changeToken pasting allows one to glue together two macro arguments. For example, front##back
yields frontback
. A famous example is Win32’s <TCHAR.H>
header. In standard C, one can write L"string"
to declare a wide character string. However, Windows API allows one to convert between wide character strings and narrow character strings simply by #define
ing UNICODE
. In order to implement the string literals, TCHAR.H
uses this
#ifdef UNICODE
#define TEXT(x) L##x
#endif
Whenever a user writes TEXT("hello, world")
, and UNICODE is defined, the C preprocessor concatenates L
and the macro argument. L
concatenated with "hello, world"
gives L"hello, world"
.
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