Tricks with Comments

Trick one: The code switch Sometimes it is essential to switch between two blocks of code. On systems that support C style comments, you could use the following construct:

//* Two slashes for version A, one slash for version B

int main() // version A
{
   printf("Version A\n");
}

/*/

int main() // version B
{
   printf("Version B\n");
}

//*/

Works on C/C++/Java/C#. For SQL:

--/*
SELECT * FROM A
/*/
SELECT * FROM B
--*/

Remove the -- on the first line to switch to the second block. Now, if anyone knows how to do it in other languages...

Trick two: Nested comments Some compilers support nested comments (actually, only Borland!). This piece of code helps you detect if the compiler supports nested comments:

#define NESTED /* /* /*/ 0 */*/*/1

main()
{
   puts(NESTED ? "Supported" : "Unsupported");
}