    #if defined _DEBUG || defined _UNIT_TEST 
      //Code here 
    #endif 

You could use AND and NOT operators as well. For instance:

    #if !defined _DEBUG &amp;&amp; defined _UNIT_TEST 
      //Code here 
    #endif 


`#if` takes _any_ C++ expression of integral type(1) that the compiler manages to evaluate at compile time. So yes, you can use `||` and `&amp;&amp;`, as long as you use `defined(SOMETHING)` to test for definedness.

(1): well, it&#39;s a bit more restricted than that; for the nitty-gritty see the restrictions [here][1] (at *&quot;with these additional restrictions&quot;*).

  [1]: https://msdn.microsoft.com/en-us/library/ew2hz0yd.aspx

    #if defined(_DEBUG) || defined(_UNIT_TEST)
      //Code here
    #endif

Also for the record, it&#39;s `#elif`, not `#elseif`.

I have a collection of boxes with the properties weight, volume and owner.

I want to use LINQ to get a summarized list (by owner) of the box information

e.g.

    **Owner, Boxes, Total Weight, Total Volume**  
    Jim,     5,     1430.00,      3.65  
    George,  2,     37.50,        1.22

Can someone show me how to do this with Lambda expressions?

Using GroupBy, Count and Sum in LINQ Lambda Expressions

I want to check if an image exists using jquery.

For example how do I check this image exists

    http://www.google.com/images/srpr/nav_logo14.png 

the check must give me a 200 or status ok


--------------edited-------------------

    var imgsrc = $(this).attr(&#39;src&#39;);
    var imgcheck = imgsrc.width;
    
    
    if (imgcheck==0) {
    alert(&quot;You have a zero size image&quot;);
    } else { //do rest of code }





Thanks
Jean


How to check if image exists with given url?

I wondering if it possible to have a preprocessor OR or AND statement?  I have this code where I want to run under `_DEBUG` or `_UNIT_TEST` tags(?).

What I want is something like the following:

    #if _DEBUG || _UNIT_TEST
      //Code here
    #endif

If this is not possible, is there a workaround to achieve the same thing without having to duplicate the code using a `#elseif`?



Can boolean operators be used with the preprocessor?

I wondering if it possible to have a preprocessor OR or AND statement? I have this code where I want to run under <code>_DEBUG</code> or <code>_UNIT_TEST</code> tags(?).
What I want is something like the following:
<pre><code class="hljs language-arduino">#if _DEBUG || _UNIT_TEST
 //Code here
#endif
</code></pre>
If this is not possible, is there a workaround to achieve the same thing without having to duplicate the code using a <code>#elseif</code>?

For any STL container that I&#39;m using, if I declare an iterator (of this particular container type) using the iterator&#39;s default constructor, what will the iterator be initialised to? 

For example, I have: 

    std::list&lt;void*&gt; address_list;
    std::list&lt;void*&gt;::iterator iter;

What will iter be initialised to? 

What is an iterator&#39;s default value?

This question is perhaps somehow odd, but how can I speed up g++ compile time? My C++ code heavily uses boost and templates. I already moved as much as possible out of the headers files and use the -j option, but still it takes quite a while to compile (and link).

Are there any tools out there which analyse my code and point out bottle-necks for the compiler? Or can one somehow profile the compiler running on my code? This would be really nice, because sometimes I have the impression, that I spent too much time staring at the compiler console log ...


How to speed up g++ compile time (when using a lot of templates)

There are (among others) two types of calling conventions - **stdcall** and **cdecl**. I have few questions on them:

 1. When a cdecl function is called, how does a caller
    know if it should free up the stack ? At the call site, does the
    caller know if the function being called is a cdecl or a stdcall
    function ? How does it work ? How does the caller know if it should
    free up the stack or not ? Or is it the linkers responsibility ?
 2. If a function which is declared as stdcall calls a function(which
    has a calling convention as cdecl), or the other way round, would
    this be inappropriate ?
 3. In general, can we say that which call will be faster - cdecl or
    stdcall ?

stdcall and cdecl

OK - I&#39;m almost embarrassed posting this here (and I will delete if anyone votes to close) as it seems like a basic question.

Is this the correct way to round up to a multiple of a number in C++? 

 I know there are other questions related to this but I am specficially interested to know what is the best way to do this in C++:

    int roundUp(int numToRound, int multiple)
    {
     if(multiple == 0)
     {
      return numToRound;
     }
    
     int roundDown = ( (int) (numToRound) / multiple) * multiple;
     int roundUp = roundDown + multiple; 
     int roundCalc = roundUp;
     return (roundCalc);
    }


Update:
Sorry I probably didn&#39;t make intention clear.  Here are some examples:

    roundUp(7, 100)
    //return 100
  
    roundUp(117, 100)
    //return 200

    roundUp(477, 100)
    //return 500

    roundUp(1077, 100)
    //return 1100

    roundUp(52, 20)
    //return 60

    roundUp(74, 30)
    //return 90

Rounding up to the nearest multiple of a number

I&#39;m wondering whether the tuple can be initialized by initializer list (to be more precise - by initializer_list of initializer_lists)? Considering the tuple definition:

    typedef std::tuple&lt; std::array&lt;short, 3&gt;,
                        std::array&lt;float, 2&gt;,
                        std::array&lt;unsigned char, 4&gt;,
                        std::array&lt;unsigned char, 4&gt; &gt; vertex;

is there any way of doing the following:

    static vertex const nullvertex = { {{0, 0, 0}},
                                       {{0.0, 0.0}},
                                       {{0, 0, 0, 0}},
                                       {{0, 0, 0, 0}} };

I just want to achieve same functionality I got using struct instead of tuple (thus only arrays are initialized by initializer_list):

    static struct vertex {
        std::array&lt;short, 3&gt; m_vertex_coords;
        std::array&lt;float, 2&gt; m_texture_coords;
        std::array&lt;unsigned char, 4&gt; m_color_1;
        std::array&lt;unsigned char, 4&gt; m_color_2;
    } const nullvertex = {
        {{0, 0, 0}},
        {{0.0, 0.0}},
        {{0, 0, 0, 0}},
        {{0, 0, 0, 0}}
    };

There is no reason I must use tuples, just wondering. I&#39;m asking, because I&#39;m unable to go through g++ templates errors which are generated by my attempt of such tuple initialization.

@Motti: So I missed the proper syntax for uniform initialization - 

    static vertex const nullvertex = vertex{ {{0, 0, 0}},
                                             {{0.0, 0.0}},
                                             {{0, 0, 0, 0}},
                                             {{0, 0, 0, 0}} };

and 

    static vertex const nullvertex{ {{0, 0, 0}},
                                    {{0.0, 0.0}},
                                    {{0, 0, 0, 0}},
                                    {{0, 0, 0, 0}} };

But it seems that all the trouble lies in arrays, which got no constructor for initializer_list and wrapping arrays with proper constructor seems not so easy task.

Initializing std::tuple from initializer list

Where are `MIN` and `MAX` defined in C, if at all?

What is the best way to implement these, as generically and type safely as possible? (Compiler extensions/builtins for mainstream compilers preferred.)

MIN and MAX in C

How do I view the output produced by the **C** pre-processor, prior to its conversion into an object file?

I want to see what the MACRO definitions do to my code.

Preprocessor output

```lang-c    
#define one 0
#ifdef one
printf(&quot;one is defined &quot;);
#ifndef one
printf(&quot;one is not defined &quot;);
```
In this what is the role of `#ifdef` and `#ifndef`, and what&#39;s the output?

The role of #ifdef and #ifndef

I&#39;m working on a project that has a lot of legacy **C** code.  We&#39;ve started writing in C++, with the intent to eventually convert the legacy code, as well.  I&#39;m a little confused about how the **C** and C++ interact.  I understand that by wrapping the **C** code with `extern &quot;C&quot;` the C++ compiler will not mangle the **C** code&#39;s names, but I&#39;m not entirely sure how to implement this.

So, at the top of each **C** header file (after the include guards), we have

    #ifdef __cplusplus
    extern &quot;C&quot; {
    #endif

and at the bottom, we write

    #ifdef __cplusplus
    }
    #endif

In between the two, we have all of our includes, typedefs, and function prototypes.  I have a few questions, to see if I&#39;m understanding this correctly:

 1. If I have a C++ file A.hh which
    includes a **C** header file B.h,
    includes another **C** header file C.h,
    how does this work?  I think that
    when the compiler steps into B.h,
    `__cplusplus` will be defined, so it
    will wrap the code with `extern &quot;C&quot;`
    (and `__cplusplus` will not be
    defined inside this block).  So,
    when it steps into C.h,
    `__cplusplus` will not be defined
    and the code will not be wrapped in
    `extern &quot;C&quot;`.  Is this correct?
    
 2. Is there anything wrong with
    wrapping a piece of code with
    `extern &quot;C&quot; { extern &quot;C&quot; { .. } }`? 
    What will the second `extern &quot;C&quot;`
    do?
    
 3. We don&#39;t put this wrapper around the .c files, just the .h files.  So, what happens if a function doesn&#39;t have a prototype? Does the compiler think that it&#39;s a C++ function?
    
 4. We are also using some third-party
    code which is written in **C**, and does
    not have this sort of wrapper around
    it.  Any time I include a header
    from that library, I&#39;ve been putting
    an `extern &quot;C&quot;` around the #include.
    Is this the right way to deal with
    that?
    
 5. Finally, is this set up a good idea?
    Is there anything else we should do?
    We&#39;re going to be mixing **C** and C++
    for the foreseeable future, and I
    want to make sure we&#39;re covering all
    our bases.

Combining C++ and C - how does #ifdef __cplusplus work?

What is the difference (if any) between the two following preprocessor control statements.

    #if

and

    #ifdef

Content Type	Original Author	Original Content on Stackoverflow
Question	Wesley	View Question on Stackoverflow
Solution 1 - C++	Kirill V. Lyadvinsky	View Answer on Stackoverflow
Solution 2 - C++	Roman Starkov	View Answer on Stackoverflow
Solution 3 - C++	AshleysBrain	View Answer on Stackoverflow

Can boolean operators be used with the preprocessor?

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Solution 3 - C++

How to check if image exists with given url?

Using GroupBy, Count and Sum in LINQ Lambda Expressions

Attributions