They are not the same. The first one doesn&#39;t work (I tested in gcc 4.4.1). Error message was:

&gt; test.cc:1:15: warning: extra tokens at
&gt; end of #ifdef directive

If you want to check if multiple things are defined, use the second one.

[Conditional Compilation][1] 

&gt; You can use the defined operator in
&gt; the #if directive to use expressions
&gt; that evaluate to 0 or 1 within a
&gt; preprocessor line. This saves you from
&gt; using nested preprocessing directives.
&gt; The parentheses around the identifier
&gt; are optional. For example:
&gt;   
&gt; 
&gt;     #if defined (MAX) &amp;&amp; ! defined (MIN)  
&gt; 
&gt; Without using the defined operator,
&gt; you would have to include the
&gt; following two directives to perform
&gt; the above example:
&gt; 
&gt;     #ifdef max 
&gt;     #ifndef min


  [1]: https://gcc.gnu.org/onlinedocs/cpp/Conditionals.html

The following results are the same:

1.

    #define A
    #define B
    #if(defined A &amp;&amp; defined B)
    printf(&quot;define test&quot;);
    #endif

2.

    #ifdef A
    #ifdef B
    printf(&quot;define test&quot;);
    #endif
    #endif

For those that might be looking for example (UNIX/g++) that is a little different from the OP, this may help:

   `

    #if(defined A &amp;&amp; defined B &amp;&amp; defined C)
        const string foo = &quot;xyz&quot;;
    #else
    #if(defined A &amp;&amp; defined B)
        const string foo = &quot;xy&quot;;
    #else
    #if(defined A &amp;&amp; defined C)
        const string foo = &quot;xz&quot;;
    #else
    #ifdef A
        const string foo = &quot;x&quot;;
    #endif
    #endif
    #endif
    #endif

As of VS2015 none of the above works. The correct directive is:

    #if (MAX &amp;&amp; !MIN)

see more [here][1]


  [1]: https://msdn.microsoft.com/en-us/library/4y6tbswk.aspx

In large and complex software products managing configurable settings becomes a major pain. Two approaches I&#39;ve seen to the problem are: 

 - have each component in the system load its own configuration from config files or registry settings. 
 - have a settings loader class that loads all the configurable system settings and have each component query the settings loader for its settings. 

These approaches both feel wrong to me. 

**Are there any design patterns that could be used to simplify the problem?** Maybe something that would take advantage of the dependency injection technique. 




Which design patterns can be applied to the configuration settings problem?

Basically I&#39;m after [this][1] but for PowerShell instead of bash.

I use git on windows through PowerShell. If possible, I&#39;d like my current branch name to displayed as part of the command prompt.


  [1]: https://stackoverflow.com/questions/816790/append-gits-branch-name-to-command-prompt

How can I display my current git branch name in my PowerShell prompt?

In C++, is this:

    #ifdef A &amp;&amp; B

the same as:
    
    #if defined(A) &amp;&amp; defined(B)

?

I was thinking it wasn&#39;t, but I haven&#39;t been able to find a difference with my compiler (VS2005).

Boolean in ifdef: is &quot;#ifdef A &amp;&amp; B&quot; the same as &quot;#if defined(A) &amp;&amp; defined(B)&quot;?

In C++, is this:
<pre><code class="hljs language-less">#ifdef A &#x26;&#x26; B
</code></pre>
the same as:
<pre><code class="hljs language-scss">#if defined(A) &#x26;&#x26; defined(B)
</code></pre>
?
I was thinking it wasn't, but I haven't been able to find a difference with my compiler (VS2005).

When I execute &quot;`python`&quot; from the terminal with no arguments it brings up the Python interactive shell.

When I execute &quot;`cat | python`&quot; from the terminal it doesn&#39;t launch the interactive mode. Somehow, without getting any input, it has detected that it is connected to a pipe.

How would I do a similar detection in C or C++ or Qt?

Detect if stdin is a terminal or pipe?

Often when iterating through a string (or any enumerable object), we are not only interested in the current value, but also the position (index). To accomplish this by using `string::iterator` we have to maintain a separate index:

 

    string str (&quot;Test string&quot;);
    string::iterator it;
    int index = 0;
    for ( it = str.begin() ; it &lt; str.end(); it++ ,index++)
    {
        cout &lt;&lt; index &lt;&lt; *it;
    }
      
The style shown above does not seem superior to the &#39;c-style&#39;:

    string str (&quot;Test string&quot;);
    for ( int i = 0 ; i &lt; str.length(); i++)
    {
        cout &lt;&lt; i &lt;&lt; str[i] ;
    }

In Ruby, we can get both content and index in a elegant way:
      
    &quot;hello&quot;.split(&quot;&quot;).each_with_index {|c, i| puts &quot;#{i} , #{c}&quot; }

So, what is the best practice in C++ to iterate through an enumerable object and also keep track of the current index?



How can I iterate through a string and also know the index (current position)?

The question I always wanted to ask and was afraid to, actually - &lt;b&gt;what language is .NET Framework written in?&lt;/b&gt; I mean library itself.&lt;br&gt;
It seems to me that it was C and C++ mostly. (I hope Jon Skeet is reading this one, it`ll be very interesting to hear what he thinks about it)

What language is .NET Framework written in?

I need to create a `GUID` in an unmanaged windows C++ project.  I&#39;m used to C#, where I&#39;d use `Guid.NewGuid()`.  What&#39;s the (unmanaged windows) C++ version?

What&#39;s the C++ version of Guid.NewGuid()?

Given the following program,

    #include &lt;iostream&gt;
    
    using namespace std;
    
    void foo( char a[100] )
    {
        cout &lt;&lt; &quot;foo() &quot; &lt;&lt; sizeof( a ) &lt;&lt; endl;
    }
    
    int main()
    {
        char bar[100] = { 0 };
        cout &lt;&lt; &quot;main() &quot; &lt;&lt; sizeof( bar ) &lt;&lt; endl;
        foo( bar );
        return 0;
    }

outputs

    main() 100
    foo() 4

 1. Why is the array passed as a pointer to the first element?
 2. Is it a heritage from C?
 3. What does the standard say?
 4. Why is the strict type-safety of C++ dropped?


When a function has a specific-size array parameter, why is it replaced with a pointer?

When learning C# for the first time, I was astonished that they had no support for macros in the same capacity that exists in C/C++. I realize that the #define keyword exists in C#, but it is greatly lacking compared to what I grew to love in C/C++. Does anyone know why **real** macros are missing from C#?

*I apologize if this question is already asked in some form or another - I promise I spent a solid 5 minutes looking for duplicates before posting.*

Why aren&#39;t there macros in C#?

I am trying to write a program where the names of some functions are dependent on the value of a certain macro variable with a macro like this:

    #define VARIABLE 3
    #define NAME(fun) fun ## _ ## VARIABLE

    int NAME(some_function)(int a);

Unfortunately, the macro `NAME()` turns that into

    int some_function_VARIABLE(int a);

rather than

    int some_function_3(int a);

so this is clearly the wrong way to go about it. Fortunately, the number of different possible values for VARIABLE is small, so I can simply do an `#if VARIABLE == n` and list all the cases separately, but is there is a clever way to do it?





How can I concatenate twice with the C preprocessor and expand a macro as in &quot;arg ## _ ## MACRO&quot;?

Consider this (horrible, terrible, no good, very bad) code structure:

    #define foo(x) // commented out debugging code

    // Misformatted to not obscure the point
    if (a)
    foo(a);
    bar(a);

I&#39;ve seen two compilers&#39; preprocessors generate different results on this code:

    if (a)
    bar(a);

and

    if (a)
    ;
    bar(a);

Obviously, this is a bad thing for a portable code base.

My question: What is the preprocessor supposed to do with this? Elide comments first, or expand macros first?

Does the C preprocessor strip comments or expand macros first?

Is it possible to make a custom operator so you can do things like this?

    if (&quot;Hello, world!&quot; contains &quot;Hello&quot;) ...

Note: this is a separate question from &quot;Is it a good idea to...&quot; ;)

Can you make custom operators in C++?

I am trying to figure out what version of Boost my code thinks it&#39;s using. I want to do something like this:

`#error BOOST_VERSION`

but the preprocessor does not expand BOOST_VERSION.

I know I could print it out at run-time from the program, and I know I could look at the output of the preprocessor to find the answer. I feel like having a way of doing this during compilation could be useful.

How do I show the value of a #define at compile-time?

I&#39;m looking for a way to reliably determine whether C++ code is being compiled in 32 vs 64 bit. We&#39;ve come up with what we think is a reasonable solution using macros, but was curious to know if people could think of cases where this might fail or if there is a better way to do this. Please note we are trying to do this in a cross-platform, multiple compiler environment.

    #if ((ULONG_MAX) == (UINT_MAX))
    # define IS32BIT
    #else
    # define IS64BIT
    #endif

    #ifdef IS64BIT
    DoMy64BitOperation()
    #else
    DoMy32BitOperation()
    #endif

Thanks.




Determining 32 vs 64 bit in C++

I doubt if there is a way to make compile-time conditions in Java like #ifdef #ifndef in C++.
  
My problem is that have an algorithm written in Java, and I have different running time improves to that algorithm. So I want to measure how much time I save when each improve is used.

Right now I have a set of boolean variables that are used to decide during the running time which improve should be used and which not. But even testing those variables influences the total running time.  

So I want to find out a way to decide during the compilation time which parts of the program should be compiled and used.  

Does someone knows a way to do it in Java. Or maybe someone knows that there is no such way (it also would be useful).

#ifdef #ifndef in Java

My project requires Java 1.6 for compilation and running. Now I have a requirement to make it working with Java 1.5 (from the marketing side). I want to replace method body (return type and arguments remain the same) to make it compiling with Java 1.5 without errors.

**Details:** I have an utility class called `OS` which encapsulates all OS-specific things. It has a method

    public static void openFile(java.io.File file) throws java.io.IOException {
      // open the file using java.awt.Desktop
      ...
    }

to open files like with double-click (`start` Windows command or `open` Mac OS X command equivalent). Since it cannot be compiled with Java 1.5, I want to exclude it during compilation and replace by another method which calls `run32dll` for Windows or `open` for Mac OS X using `Runtime.exec`.

**Question: How can I do that? Can annotations help here?**

Note: I use ant, and I can make two java files `OS4J5.java` and `OS4J6.java` which will contain the `OS` class with the desired code for Java 1.5 and 1.6 and copy one of them to `OS.java` before compiling (or an ugly way - replace the content of `OS.java` conditionally depending on java version) but I don&#39;t want to do that, if there is another way.

Elaborating more: in C I could use `ifdef, ifndef`, in Python there is no compilation and I could check a feature using `hasattr` or something else, in Common Lisp I could use `#+feature`. Is there something similar for Java?

Found [this post](https://stackoverflow.com/questions/1922521/conditional-java-compilation) but it doesn&#39;t seem to be helpful.

Any help is greatly appreciated. kh.


Java conditional compilation: how to prevent code chunks from being compiled?

I want to run some c++ code on Linux and Windows.  There are some pieces of code that I want to include only for one operating system and not the other.  Is there a standard *#ifdef* that once can use?

Something like:

      #ifdef LINUX_KEY_WORD
        ... // linux code goes here.
      #elif WINDOWS_KEY_WORD
        ... // windows code goes here.
      #else 
      #error &quot;OS not supported!&quot;
      #endif


----------
The question is indeed a duplicate but the answers here are much better, especially the accepted one.

C++ compiling on Windows and Linux: ifdef switch

Does C# have a *not* `Conditional` (`!Conditional`, `NotConditional`, `Conditional(!)`) attribute?


----------


i know C# has a [`Conditional` attribute][1]:

    [Conditional(&quot;ShowDebugString&quot;)]
    public static void ShowDebugString(string s)
    {
       ...
    }

which is equivalent&lt;sup&gt;1&lt;/sup&gt; to:

    public static void ShowDebugString(string s)
    {
    #if ShowDebugString
       ...
    #endif
    }

But in this case i want the *inverse* behavior (you have to specifically *opt out*):


    public static void ShowDebugString(string s)
    {
    #if !RemoveSDS
       ...
    #endif
    }

Which leads me to try:


    [!Conditional(&quot;RemoveSDS&quot;)]
    public static void ShowDebugString(string s)
    {
       ...
    }

which doesn&#39;t compile. And:


    [Conditional(&quot;!RemoveSDS&quot;)]
    public static void ShowDebugString(string s)
    {
       ...
    }

which doesn&#39;t compile. And:


    [NotConditional(&quot;RemoveSDS&quot;)]
    public static void ShowDebugString(string s)
    {
       ...
    }

which doesn&#39;t compile because it&#39;s only wishful thinking.

&lt;sup&gt;1&lt;/sup&gt; [Not true, but true enough. Don&#39;t make me bring back the Nitpicker&#39;s Corner.][2] &lt;sup&gt;[&#128343;][3]&lt;/sup&gt;


  [1]: https://msdn.microsoft.com/en-us/library/system.diagnostics.conditionalattribute
  [2]: http://blogs.msdn.com/b/oldnewthing/archive/2011/11/07/10234436.aspx
  [3]: https://web.archive.org/web/20111110161740/http://blogs.msdn.com/b/oldnewthing/archive/2011/11/07/10234436.aspx

Content Type	Original Author	Original Content on Stackoverflow
Question	criddell	View Question on Stackoverflow
Solution 1 - C++	Evan Teran	View Answer on Stackoverflow
Solution 2 - C++	Svetlozar Angelov	View Answer on Stackoverflow
Solution 3 - C++	way good	View Answer on Stackoverflow
Solution 4 - C++	MikeB	View Answer on Stackoverflow
Solution 5 - C++	Fabri	View Answer on Stackoverflow

Boolean in ifdef: is "#ifdef A && B" the same as "#if defined(A) && defined(B)"?

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Solution 3 - C++

Solution 4 - C++

Solution 5 - C++

How can I display my current git branch name in my PowerShell prompt?

Which design patterns can be applied to the configuration settings problem?

Attributions