Re: Compile error about MACRO

Thanks Norbert,


I am using Visual Studio 2005, are there any tools or compiler option which
could see the preprocessor processing result of a source file?


regards,
George

"Norbert Unterberg" wrote:

George schrieb:

The compile error of the following code is,

foo.cpp(7) : error C2146: syntax error : missing ';' before identifier '_'
foo.cpp(7) : error C2065: '_' : undeclared identifier
foo.cpp(7) : error C2143: syntax error : missing ';' before 'string'

I do not know why there is errors. I think in MERGE macro, the value of
parameter a is hello and the value of parameter b is world in my case, and I
defined hello_world to "H E L L O", it should be fine...

Wrong. In the MERGE macro, a is replaced by the string "hello", not the token
hello. You only use quotes in macro arguments when you want strings.


Any ideas?

[Code]
#define MERGE(a,b) a ## _ ## b
#define hello_world "H E L L O"

int foo()
{
char* p0;
p0 = MERGE("hello", "world");

This expands to:
p0 = "Hello"_"world";

which is definately a syntax error. Try:
p0 = MERGE(hello, world);

You are just experiencing the difference between a string and a token. The ##
operator works on tokens not on strings. To merge strings you do not need the ##
operator.

Norbert


.

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