Gold mine of Visual C++ tricks!
How to get the preprocessed C / C++ source files?
Everybody knows that before the real compilation, the source file will undergo the stage called preprocessing. All the compiler preprocessors such as #include, #define etc will be processed in this stage and that intermediate preprocessed file, which is the real source – will be fed to compiler for compiling. Its a bit difficult to troubleshoot problems with preprocessor( especially macro expansions ) because, the processed intermediate file is not available. But is to possible to get it?
Ofcourse. You can use the compiler option /P. Take the project settings, In the C/C++ tab add the /P to compiler options. See the screenshot below.
Now if you take your source folder, you can see files with extension *.i
So if you’ve some trouble in macro expansion, just generate the intermediate file and check.
Open the generated intermediate file and see the contents. I’m sure you can’t believe your eyes. 
Targeted Audience – Beginners.
| Print article | This entry was posted by Jijo Raj on June 12, 2008 at 6:05 pm, and is filed under Compiler Extension. Follow any responses to this post through RSS 2.0. You can leave a response or trackback from your own site. |
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Visual C++ Preprocessor null directive
about 2 years ago - No comments
Well, add an empty # symbol to your #include list and compile the project. For e.g. see the following #include list.
#include “stdafx.h”
#include “Dialog.h”
#
#include “DialogDlg.h”
It will compile without showing any errors. Weird?
The single “#” in a line is called null directive. It has no effect. Indeed, its not a bug.
But i can’t find
Log path informations to eventlog, Even better.
about 2 years ago - No comments
In most of our projects, when some error occurs, it’s being logged to the evenlog with line number and filename. Its done by using __FILE__ and __LINE__ macro.
But the file macros expands to the fullpath. for e.g. If i am building the delivery in my personal folder – “C:\Jijo\Build\MyProduct”, the __FILE__ macro will include this
about 2 years ago
Really nice and useful tip.
But got link error when I used that. I created a dlg based app. And given the /P option and built the source. Then I got a link error LINK : fatal error LNK1104: cannot open file “.\Debug\PreProcExp.obj”
If I remove the /P option then I will get the build successfully.
Anyway I could see the intermediate macro expanded files…
about 2 years ago
Nishad, You are right. Me too had the same link error. But the intermediate files are generated. Happy to know that the /P serve your need.
about 2 years ago
During this process actual object file generation is not done. Thats why the link error. This /P flag can be used evenif some compilation errors are present in the source file
So this flag is only checking the preprocessed output of an input file.
about 2 years ago
So this flag is used only for checking the preprocessed output of an input file.
about 1 year ago
It would be highly desirable for the IDE to generate the preprocessed output in a specified (fixed name) file and then continue with the compiling and linking process without resulting later in link errors as reported here. By default, the file would contain the preprocessed output of the last file compiled. With this approach, resources available for debugging a program would include this valuable preprocessed information without the need to set up switches or other complications such as linking errors downstream.