Solved

ifdef

Posted on 2011-03-21
7
455 Views
Last Modified: 2012-05-11
#ifdef TEST
            // Line 1
#else
           // Line 1
#endif

What if I need multiple lines. is it possible
0
Comment
Question by:learningunix
7 Comments
 
LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 250 total points
ID: 35184506
Yes. Everything between the #ifdef and the #endif will be treated as one unit. It is much like a regular "if" statement, but you can think of the #endif as being a substitute for the curly braces.
0
 
LVL 16

Expert Comment

by:imladris
ID: 35184509
Yup. You can have as many lines as you like. That why the #else and the #endif are there. They are used to mark the end of the conditional code. In fact, internally, C and C++ don't even "see" lines. It's just one long string of characters. To the parser, newlines, which define the end of lines, are just characters to be ignored like blanks.
0
 
LVL 86

Expert Comment

by:jkr
ID: 35184513
Absolutely - actually, that's quite common. Most header files are secured via header guards (http://faculty.cs.niu.edu/~mcmahon/CS241/c241man/node90.html), so that's not only more than one line, but merely a whole file.
0
Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

 

Author Comment

by:learningunix
ID: 35185640
Ok. I thought I have to use { } for multiple lines but that is not the case

This should work

#ifdef TEST
            int a = 1;
            a++;
           printf ("%d"a);            
#else
           // Line 1
           // Line 2
#endif

0
 
LVL 86

Expert Comment

by:jkr
ID: 35186117
That should definitely work. Just keep in mind that e.g. a #define statement spanning multiple lines needs a trailing backslash if you want to do something like this.
0
 
LVL 33

Expert Comment

by:sarabande
ID: 35187657
you sometimes will see in code

#if  1
   // some code

#endif

the 1 means true and it is easily changed to #if 0 if the code shouldn't be performed anymore. using constants instead of preprocessor macros has advantages for temporary code and code limited to one source cause you don't need to define/undefine a macro like TEST..

Sara
0
 

Author Closing Comment

by:learningunix
ID: 35227103
thx
0

Featured Post

Free Tool: ZipGrep

ZipGrep is a utility that can list and search zip (.war, .ear, .jar, etc) archives for text patterns, without the need to extract the archive's contents.

One of a set of tools we're offering as a way to say thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
mixing C++ & C# in Vis Studio 2013 7 195
convert char array to number in c 5 86
DCT of  2D array using fftw in c++ 9 61
C++ Code Issue 4 22
When writing generic code, using template meta-programming techniques, it is sometimes useful to know if a type is convertible to another type. A good example of when this might be is if you are writing diagnostic instrumentation for code to generat…
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

791 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question