You can&#39;t do that. You have to do something like this:

    #ifdef DEBUG
    #define DO(WHAT) MyObj-&gt;WHAT()
    #else
    #define DO(WHAT) do { } while(0)
    #endif

The `do { } while(0)` avoids empty statements. See [this question][1], for example.


  [1]: https://stackoverflow.com/questions/923822/whats-the-use-of-do-while0-when-we-define-a-macro

It screams because you can&#39;t do that.

I suggest the following as an alternative:

    #ifdef DEBUG
    #define DO(WHAT) MyObj-&gt;WHAT()
    #else
    #define DO(WHAT)
    #endif

It seems that what you want to do can be achieved like this, without running into any problems:

    #ifdef DEBUG
    #    define DO(WHAT) MyObj-&gt;WHAT()
    #else
    #    define DO(WHAT) while(false)
    #endif

Btw, better use the `NDEBUG` macro, unless you have a more specific reason not to. `NDEBUG` is more widely used as a macro that means no-debugging. For example the standard [`assert`](http://www.cplusplus.com/reference/clibrary/cassert/assert/) macro can be disabled by defining `NDEBUG`. Your code would become:


    #ifndef NDEBUG
    #    define DO(WHAT) MyObj-&gt;WHAT()
    #else
    #    define DO(WHAT) while(false)
    #endif

You can do the same thing like this:

    #ifdef DEBUG
    #define DO(WHAT) MyObj-&gt;WHAT()
    #else
    #define DO(WHAT)
    #endif

How about:

    #ifdef DEBUG
    #define DO(WHAT) MyObj-&gt;WHAT()
    #else
    #define DO(WHAT)
    #endif



I made a table using SQLAlchemy and forgot to add a column. I basically want to do this:

    users.addColumn(&#39;user_id&#39;, ForeignKey(&#39;users.user_id&#39;))

What&#39;s the syntax for this? I couldn&#39;t find it in the docs.

add column to SQLAlchemy Table

The look of a WPF CheckBox misaligns the check portion with the label (content) portion. The check stays slightly above the content as shown here:

![enter image description here][1]

The XAML looks like this:

    &lt;CheckBox Content=&quot;Poorly aligned CheckBox&quot; Margin=&quot;9&quot;/&gt;

The CheckBox is inside a Grid cell. **Is there a simple way to make the content and check portions of a XAML CheckBox align vertically?** I&#39;ve tried various combinations of properties with no luck. I saw [a similar question here][2] but the answer is way too complex.

Thanks in advance.

**EDIT: The problem was caused by the Window FontSize which I set to 14**. To re-create the problem set the CheckBox FontSize to 14 (or more). My program is viewed at a distance by factory workers so I allow the Window FontSize to be increased or decreased by the user.


  [1]: http://i.stack.imgur.com/cTT3O.png
  [2]: https://stackoverflow.com/questions/6077510/how-can-i-center-a-wpf-checkbox-inside-its-clickable-region

How can I align a CheckBox with its content?

&gt; **Possible Duplicate:**  
&gt; [#ifdef inside #define](https://stackoverflow.com/questions/5586429/ifdef-inside-define)  

&lt;!-- End of automatically inserted text --&gt;

How do I use the character &quot;#&quot; successfully inside a Macro? It screams when I do something like that:

    #define DO(WHAT)        \
    #ifdef DEBUG		\							
      MyObj-&gt;WHAT()	        \		
    #endif	         	\

							


&quot;#ifdef&quot; inside a macro

> Possible Duplicate: 
> <a href="https://stackoverflow.com/questions/5586429/ifdef-inside-define" target="_blank" rel="noopener noreferrer">#ifdef inside #define</a>

How do I use the character "#" successfully inside a Macro? It screams when I do something like that:
<pre><code class="hljs language-arduino">#define DO(WHAT) \
#ifdef DEBUG		\							
 MyObj->WHAT()	 \		
#endif	 	\

						
</code></pre>

This C++ program is a CGI script, I have no desire to deal with exceptions. I&#39;d rather get a marginal performance boost and let the OS (Linux) handle cleanup after the process dies.

I am using the Standard C++ Library, and want any function to `die` like in Perl: **Whenever it throws an exception.** Without unwinding, *or running any further code* in my process.

How does -fno-exceptions work? If I have no catch at all in my code, and basically pretend like exceptions do no exist. but I **do** use std:: c++ library which **can** throw()?

Disabling C++ exceptions, how can I make any std:: throw() immediately terminate?

C++0x shows an example of using `std::forward`:

    template&lt;class T&gt;
    void foo(T&amp;&amp; arg) 
    {
      bar(std::forward&lt;T&gt;(arg));
    }

When is it advantageous to use `std::forward`, always?

Also, it requires to use `&amp;&amp;` in the parameters declaration, is it valid in all cases? I thought you had to pass temporaries to a function if the function was declared with `&amp;&amp;` in it, so can foo be called with any parameter?

Lastly, if I have a function call such as this:

    template&lt;int val, typename... Params&gt;
    void doSomething(Params... args) {
      doSomethingElse&lt;val, Params...&gt;(args...);
    }

Should I use this instead:

    template&lt;int val, typename... Params&gt;
    void doSomething(Params&amp;&amp;... args) {
      doSomethingElse&lt;val, Params...&gt;(std::forward&lt;Params&gt;(args)...);
    }

Also, if use the parameters twice in the function, i.e. forwarding to two functions at the same time, is it wise to use `std::forward`? Won&#39;t `std::forward` convert the same thing to a temporary twice, moving the memory and make it invalid for a second use? Would the following code be ok:

    template&lt;int val, typename... Params&gt;
    void doSomething(Params&amp;&amp;... args) {
      doSomethingElse&lt;val, Params...&gt;(std::forward&lt;Params&gt;(args)...);
      doSomethingWeird&lt;val, Params...&gt;(std::forward&lt;Params&gt;(args)...);
    }

I&#39;m a bit confused by `std::forward`, and I&#39;d gladly use some clearing up.

When to use std::forward to forward arguments?

I was wondering if someone could explain there terms since I encounter them in many places. I know some basic theory about them but not sure what I know is right or wrong.

So can any one please explain these terms?


What are qualified-id/name and unqualified-id/name?

I am trying to compile a simple VS program in C++ as an assignment for class. We only ever include `&lt;iostream&gt;` and I keep getting this error:

&gt;1&gt;Assignment.cpp(15): fatal error C1010: unexpected end of file while looking for precompiled header. Did you forget to add `&#39;#include &quot;StdAfx.h&quot;&#39;` to your source?

My program is literally this small...

    #include &lt;iostream&gt;
    using namespace std;
    int main()
    {
        unsigned int day = 30;

        cout &lt;&lt; &quot;My Name is John Doe&quot; &lt;&lt; endl;
        cout &lt;&lt; &quot;My Major is CS&quot; &lt;&lt; endl;
        cout &lt;&lt; &quot;I was born on day &quot; &lt;&lt; day &lt;&lt; endl;
        return 0;
    }

I just installed Visual Studio Express 2010. Really I would love to start an empty project instead of installing with all these files predefined, I think it would make it a lot easier but I never get that option when creating a project. Anybody have any suggestions?

How to avoid precompiled headers

I&#39;ve been looking around for this one, and the common response to this seems to be along the lines of &quot;they are unrelated, and one can&#39;t be substituted for the other&quot;. But say you&#39;re in an interview and get asked &quot;When would you use a template instead of inheritance and vice versa?&quot;

When to use template vs inheritance

I have a main directory `A` with two sub directories `B` and `C`.

Directory `B` contains a header file `structures.c`:
                        
    #ifndef __STRUCTURES_H
    #define __STRUCTURES_H
    typedef struct __stud_ent__
    {
        char name[20];
        int roll_num;
    }stud;
    #endif


Directory `C` contains `main.c` code:

    #include&lt;stdio.h&gt;
    #include&lt;stdlib.h&gt;
    #include &lt;structures.h&gt;
    int main()
    {
        stud *value;
        value = malloc(sizeof(stud));
        free (value);
        printf(&quot;working \n&quot;);
        return 0;
    }

But I get an error:

&lt;!-- language: none --&gt; 

    main.c:3:24: error: structures.h: No such file or directory
    main.c: In function ‘main’:
    main.c:6: error: ‘stud’ undeclared (first use in this function)
    main.c:6: error: (Each undeclared identifier is reported only once
    main.c:6: error: for each function it appears in.)
    main.c:6: error: ‘value’ undeclared (first use in this function)

What is the correct way to include the `structures.h` file into `main.c`?

Including a header file from another directory


What I&#39;m trying to figure out is if something such as this (written in **C**):

    #define FOO 15
    #define BAR 23
    #define MEH (FOO / BAR)

is allowed?  I would want the preprocessor to replace every instance of

    MEH

with

    (15 / 23)

but I&#39;m not so sure that will work.  Certainly if the preprocessor only goes through the code once then I don&#39;t think it&#39;d work out the way I&#39;d like.

I found several similar examples but all were really too complicated for me to understand.  If someone could help me out with this simple one I&#39;d be eternally grateful!



Can a C macro definition refer to other macros?

Shortly, I want to know if gcc (or g++. I need it in **C**, but also am curious about c++) defines any special symbols if `-g` is enabled. Does it? If so, what symbols?

In the search process I found out that:

- `_DEBUG` is defined manually (by manually I mean `-D_DEBUG`) and is a habit taken from Visual C programmers  (because VC defines `_DEBUG` when compiling in debug mode)
- `NDEBUG` is defined if NOT in debug mode. Although I found a few places saying this, I tried with my gcc and g++ in .c and .cpp files and in none of them with or without `-g` no such symbol was defined!

**Edit**: Let me demonstrate why I don&#39;t want to use a non-standard symbol:

Imagine a kernel module that does something and also provides header files to be included in other kernel modules so that they can connect to this one.

Now as a facility, in one of the header files I have:

    #ifdef DEBUG &lt;-- This is what I need
    #define LOG(x, ...) printk(&quot;Some extra info&quot;x, ##__VA_ARGS__);
    #else
    #define LOG(x, ...) printk(&quot;Without extra info&quot;x, ##__VA_ARGS__);
    #endif

Note that the name is not really `LOG`, that&#39;s an example.

Now, I can use any symbol for `DEBUG` myself, but then if someone includes my header, they may not define that symbol. Of course I can tell them &quot;by the way, to get the headers in debug mode, define this other symbol&quot;, but that just doesn&#39;t sound right to me.

I could define the symbol in a header and include it in all header files. This way, if they include one of my headers, they get the debug symbol too. The problem now is that, if they _don&#39;t_ want to compile in debug mode, my headers still think they are in debug mode.

So what I thought would be best was to use a symbol that is defined when `-g` is used, if there are any!

## Update

So far I came to the conclusion that I could do something like this:

how_to_build.h

    #if !defined(NDEBUG)
    #define MY_DEBUG
    #endif

Usage:

    #include &quot;how_to_build.h&quot;

    #ifdef MY_DEBUG
    // rest of the story

This way, the common option of `NDEBUG` removes my definition also. It still requires me to tell them to define it if they don&#39;t want to get the headers in debug mode.

Does gcc define anything when -g is specified?

If I have:

    #define MAXLINE    5000

What type is MAXLINE understood to be? Should I assume it is an `int`? Can I test it somehow?

In general, how can one determine the type of `#define`ed variable?

Type of #define variables

How do I define a preprocessor variable through CMake?

The equivalent code would be `#define foo`.

Content Type	Original Author	Original Content on Stackoverflow
Question	JasonGenX	View Question on Stackoverflow
Solution 1 - C++	Roger Lipscombe	View Answer on Stackoverflow
Solution 2 - C++	Oliver Charlesworth	View Answer on Stackoverflow
Solution 3 - C++	Paul Manta	View Answer on Stackoverflow
Solution 4 - C++	antlersoft	View Answer on Stackoverflow
Solution 5 - C++	Miguel Grinberg	View Answer on Stackoverflow

"#ifdef" inside a macro

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Solution 3 - C++

Solution 4 - C++

Solution 5 - C++

How can I align a CheckBox with its content?

add column to SQLAlchemy Table

Attributions