Try setting `C_INCLUDE_PATH` (for C header files) or `CPLUS_INCLUDE_PATH` (for C++ header files).

As Ciro mentioned, `CPATH` will set the path for both C and C++ (and any other language).

More details in [GCC&#39;s documentation][1].


  [1]: https://web.archive.org/web/20090129230009if_/http://www.network-theory.co.uk/docs/gccintro/gccintro_23.html

Create an alias for gcc with your favorite includes.

    alias mygcc=&#39;gcc -I /whatever/&#39;


just a note: `CPLUS_INCLUDE_PATH` and `C_INCLUDE_PATH` are not the equivalent of `LD_LIBRARY_PATH`.
`LD_LIBRARY_PATH` serves the `ld` (the dynamic linker at runtime) whereas the equivalent of the former two that serves your C/C++ compiler with the location of libraries is `LIBRARY_PATH`.

A gcc spec file can do the job, however all users on the machine will be affected.

See [HOWTO Use the GCC specs file][1]


  [1]: https://web.archive.org/web/20200616193104/http://www.mingw.org/node/25

Having a look on the PHP documentation, the following two methods of the `DateTime` object would both seem to solve my problem:

- &lt;a href=&quot;http://au.php.net/manual/en/datetime.diff.php&quot;&gt;DateTime::diff&lt;/a&gt; : Get the difference and use that to determine which is more ancient.
- &lt;a href=&quot;http://au.php.net/manual/en/datetime.gettimestamp.php&quot;&gt;DateTime::getTimestamp&lt;/a&gt; : Get the UNIX timestampt and compare those.

Both these methods are marked in the &lt;a href=&quot;http://au.php.net/datetime&quot;&gt;doco&lt;/a&gt; as being available in version &gt;= 5.3 (and, not surprisingly, if I try to call them I find they don&#39;t exist). I can&#39;t find any specific documentation for 5.2.8 so I am not sure if there are equivalent methods in my version.  I have &lt;a href=&quot;http://www.google.com.au/search?q=compare+DateTime+PHP&amp;ie=utf-8&amp;oe=utf-8&amp;aq=t&amp;rls=org.mozilla:en-US:official&amp;client=firefox-a&quot;&gt;Googled&lt;/a&gt; the problem and found an eclectic range of solutions, none of which answer my very simple requirements:

- How do I compare two DateTime objects?
- Where can I find the doco for previous PHP versions? Specifically version 5.2.8?

For some context, I have the following code:

    $st_dt = new DateTime(verifyParam (&#39;start_date&#39;));
    $end_dt = new DateTime(verifyParam (&#39;end_date&#39;));

    // is the end date more ancient than the start date?
    if ($end_dt &lt; $start_dt) 

Apparently there is no comparison operator on this guy.  

Edit
---

*Apparently* my assumptions were completely false (thanks Milen for illustrating this so effectively).  There is a comparison operator and it works just fine thanks.  Sometimes I really miss a compiler.  The bug is in the code above, I am sure you will find it much faster than I did :).


How do I compare two DateTime objects in PHP 5.2.8?

Let&#39;s say I have a class called `SomeClass` with a `string` property name:

    @interface SomeClass : NSObject
    {
        NSString* name;
    }
    
    @property (nonatomic, retain) NSString* name;
    
    @end

I understand that name may be assigned a `NSMutableString` in which case this may lead to errant behavior. 

* For strings in general, is it *always* a good idea to use the `copy` attribute instead of `retain`? 
* Is a &quot;copied&quot; property in any way less efficient than such a &quot;retain-ed&quot; property?


NSString property: copy or retain?

I&#39;d like gcc to include files from `$HOME/include` in addition to the usual include directories, but there doesn&#39;t seem to be an analogue to `$LD_LIBRARY_PATH`.

I know I can just add the include directory at command line when compiling (or in the makefile), but I&#39;d really like a universal approach here, as in the library case.

How to add a default include path for GCC in Linux?

<p>I'd like gcc to include files from <code>$HOME/include</code> in addition to the usual include directories, but there doesn't seem to be an analogue to <code>$LD_LIBRARY_PATH</code>.</p>
<p>I know I can just add the include directory at command line when compiling (or in the makefile), but I'd really like a universal approach here, as in the library case.</p>


I have a problem with a Java application running under Linux.

When I launch the application, using the default maximum heap size (64 MB), I see using the tops application that 240 MB of virtual Memory are allocated to the application.  This creates some issues with some other software on the computer, which is relatively resource-limited.

The reserved virtual memory will not be used anyway, as far as I understand, because once we reach the heap limit an `OutOfMemoryError` is thrown.  I ran the same application under windows and I see that the Virtual Memory size and the Heap size are similar.

Is there anyway that I can configure the Virtual Memory in use for a Java process under Linux?

**Edit 1**: The problem is not the Heap.  The problem is that if I set a Heap of 128 MB, for example, still Linux allocates 210 MB of Virtual Memory, which is not needed, ever.**

**Edit 2**: Using `ulimit -v` allows limiting the amount of virtual memory.  If the size set is below 204 MB, then the application won&#39;t run even though it doesn&#39;t need 204 MB, only 64 MB.  So I want to understand why Java requires so much virtual memory.  Can this be changed?

**Edit 3**: There are several other applications running in the system, which is embedded. And the system does have a virtual memory limit (from comments, important detail).

Virtual Memory Usage from Java under Linux, too much memory used

Is there a way in python to programmatically determine the width of the console? I mean the number of characters that fits in one line without wrapping, not the pixel width of the window.

&lt;b&gt;Edit&lt;/b&gt;

Looking for a solution that works on Linux

How to get Linux console window width in Python

I was just wondering who knows what programming languages Windows, Mac OS X and Linux are made up from and what languages are used for each part of the OS (ie: Kernel, plug-in architecture, GUI components, etc).

I assume that there are multiple languages for each and obviously I know the Linux kernel is written in C.

I&#39;m totally guessing here that Mac OS X contains a lot of Objective-C code as it is Apple&#39;s language derived from NeXT.

Windows, I have heard contains C, C++ and Intel Assembly. Do Linux or Mac OS contain any Assembly code?

Also, are there scripting languages like Ruby, Python, etc used by the OS developers for scripting parts of the OS? What parts of the OS would be written in each language?

What languages are Windows, Mac OS X and Linux written in?

I have a bunch of long-running scripts and applications that are storing output results in a directory shared amongst a few users. I would like a way to make sure that every file and directory created under this shared directory automatically had `u=rwxg=rwxo=r` permissions.

I know that I could use `umask 006` at the head off my various scripts, but I don&#39;t like that approach as many users write their own scripts and may forget to set the umask themselves.

I really just want the filesystem to set newly created files and directories with a certain permission if it is in a certain folder. Is this at all possible? 

**Update**: I *think* it can be done with [POSIX ACLs][1], using the Default ACL functionality, but it&#39;s all a bit over my head at the moment. If anybody can explain how to use Default ACLs it would probably answer this question nicely.


  [1]: http://www.vanemery.com/Linux/ACL/POSIX_ACL_on_Linux.html

Setting default permissions for newly created files and sub-directories under a directory in Linux?

I&#39;m looking to add a `crontab` entry to execute a script every 30 minutes, on the hour and 30 minutes past the hour or something close. I have the following, but it doesn&#39;t seem to run on 0.

    */30 * * * *

What string do I need to use?

The cron is running on OSX.

How would I get a cron job to run every 30 minutes?

I&#39;m trying to compile a simple app with gcov and getting the following link errors:

    gcc AllTests.o CuTestTest.o CuTest.o -o TestTest
    AllTests.o: In function `global constructors keyed to 0_RunAllTests&#39;:
    /home/p7539c/cutest/AllTests.c:26: undefined reference to `__gcov_init&#39;
    AllTests.o:(.data+0x44): undefined reference to `__gcov_merge_add&#39;
    CuTestTest.o: In function `global constructors keyed to 0_TestCuStringNew&#39;:
    /home/p7539c/cutest/CuTestTest.c:30: undefined reference to `__gcov_init&#39;
    CuTestTest.o:(.data+0x64): undefined reference to `__gcov_merge_add&#39;
    CuTest.o: In function `global constructors keyed to 0_CuStrAlloc&#39;:
    /home/p7539c/cutest/CuTest.c:379: undefined reference to `__gcov_init&#39;
    CuTest.o:(.data+0x184): undefined reference to `__gcov_merge_add&#39;
    collect2: ld returned 1 exit status
    make: *** [TestTest] Error 1

I can&#39;t seem to find the location of the missing symbols. gcov is present on the machine running gcc version 4.1.2

Any ideas? Thanks.

On Edit:

Everything seems to work fine when using gcov with an application that consists of one .c file. When I have multiple .c files (hence multiple .o files) I have the above problem.

The compile steps look like the following:

    cc -fprofile-arcs -ftest-coverage -g   -c -o AllTests.o AllTests.c
    cc -fprofile-arcs -ftest-coverage -g   -c -o CuTestTest.o CuTestTest.c
    cc -fprofile-arcs -ftest-coverage -g   -c -o CuTest.o CuTest.c

Where are the gcov symbols?

When we are compiling a C program the output is stored in a.out. How can we redirect the compiled output to another file?


Determining C executable name

What is the difference between these two file types. I see that my C++ app links against both types during the construction of the executable. 

How to build .a files? links, references, and especially examples, are highly appreciated.

.o files vs .a files

When I use gcc to compile C programs
I usually use `-g` to get some debug information into the elf file 
so that gdb can help me if needed.

However, I noticed that some programs use `-ggdb`, since it&#39;s supposed to make the 
debug info more gdb friendly. 

How do they differ and which is recommended to use?

---

*Note:* A link to the options for Debugging Your Program or GCC, http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html#Debugging-Options

What is the difference between gcc -ggdb and gcc -g

In Windows, using mingw&#39;s gcc, is there anyway to specify that the output exe file is to take an icon file, so that the exe file shows with that icon in explorer?

How do I add an icon to a mingw-gcc compiled executable?

I&#39;ve reviewed questions [How to use include directive correctly][1] and [C++ #include semantics][2] and neither addresses this - nor do the others suggested by SO when I typed the title...

What, if any, are the benefits of writing:

    #include &quot;../include/someheader.h&quot;
    #include &quot;../otherdir/another.h&quot;

compared with using just a plain file name:

    #include &quot;someheader.h&quot;
    #include &quot;another.h&quot;

or perhaps a relative name without the &#39;`..`&#39;:

    #include &quot;include/someheader.h&quot;
    #include &quot;otherdir/another.h&quot;

The problems I see are:

* You can&#39;t move a header without worrying about which source files include it.
* You can end up with very long paths for headers in dependencies and error reports.  I had one today with &quot;`../dir1/include/../../include/../dir2/../include/header.h`&quot;.

The only merit I can see is that while you do not need to move files around, you might be able to get away without always using &#39;`-I`&#39; directives to find headers, but the loss of flexibility, and the complexity of compiling in sub-sub-directories, etc seems to outweigh the benefit.

So, am I overlooking a benefit?

&lt;hr&gt;

Thanks for the inputs.  I think the consensus is that there aren&#39;t any major benefits to the notation using &quot;..&quot; that I&#39;m overlooking.  In general terms, I like the &quot;somewhere/header.h&quot; notation; I do use it in new projects.  The one I&#39;m working on is anything but new.

One of the problems is that there are various sets of headers, often with a prefix such as `rspqr.h`, `rsabc.h`, `rsdef.h`, `rsxyz.h`.  These are all related to code in the `rsmp` directory, but some of the headers are in `rsmp` and others are in the central include directory, which does not have sub-directories such as `rsmp` in it.  (And repeat for the various other areas of the code; there are headers in multiple locations, needed randomly by other bits of code.)  Moving stuff around is a major problem because the code has gotten so convoluted over the years.  And the makefiles are not consistent in which `-I` options are provided.  All in all, it is a sad story of not-so-benign neglect over a period of decades.  Fixing it all without breaking anything is going to be a long, tedious job.


  [1]: https://stackoverflow.com/questions/464560/how-to-use-include-directive-correctly
  [2]: https://stackoverflow.com/questions/179213/c-include-semantics

What are the benefits of a relative path such as &quot;../include/header.h&quot; for a header?

In PHP can I include a directory of scripts?

i.e. Instead of:

    include(&#39;classes/Class1.php&#39;);
    include(&#39;classes/Class2.php&#39;);

is there something like:

    include(&#39;classes/*&#39;);

Couldn&#39;t seem to find a good way of including a collection of about 10 sub-classes for a particular class.

How to include() all PHP files from a directory?

I often find that the headers section of a file get larger and larger all the time but it never gets smaller. Throughout the life of a source file classes may have moved and been refactored and it&#39;s very possible that there are quite a few `#includes` that don&#39;t need to be there and anymore. Leaving them there only prolong the compile time and adds unnecessary compilation dependencies. Trying to figure out which are still needed can be quite tedious.

Is there some kind of tool that can detect superfluous #include directives and suggest which ones I can safely remove?  
Does lint do this maybe?

Detecting superfluous #includes in C/C++?

I would like to include script files with such pseudo syntax:

    Include &#39;.\scripA.ps1&#39;

But the only thing I have found is some thing like this:

    $thisScript = Split-Path -Path $MyInvocation.MyCommand.Definition -Parent
    . ($thisScript + &#39;.\scriptA.ps1&#39;)

that is ugly. 

Is there some *nice* way to include scripts with relative paths?

Include relative files in PowerShell

Because I&#39;ve made .cpp files then transfered them into .h files, the only difference I can find is that you can&#39;t #include .cpp files.  Is there any difference that I am missing?

What is the difference between a .cpp file and a .h file?

I found it is hard to keep my environment variables sync on different machines. I just want to export the settings from one computer and import to other ones. 

I think it should be possible, but don&#39;t know how to do it. Can anyone help me? Thanks. 


How to export and import environment variables in windows?

I need to access an environment variable remotely. To do this, I think the best way is to read it from registry.

Where are environment variables stored in the Windows Registry?




Where are environment variables stored in the Windows Registry?

Is it possible to set an environment variable at runtime from a Java
application?
In Java 1.5 java.lang.System class there is the getenv() method, I would
only need a setenv() method...

Is it possible to modify the environment variables in the java process itself; not in the child process.

Is it possible to achieve it through JNI? And how would that work?

Thanks.

EDIT:
Ok let me put it this way - Can we do the following with Java. Please answer.

1. Can we modify the environment of the current process?
2. Can we modify the environment of the parent process?
3. Can we modify the environment of the child process?

Hemal Pandya has answered that &quot;You can modify the environment of current and child processes but not of the parent process that spawned this process.&quot; Do you agree with this ?

Is it possible to set an environment variable at runtime from Java?

Update: The link below *does not have a complete answer*. Having to set the path or variable in two places (one for GUI and one for shell) is lame.

**Not Duplicate of**: [https://stackoverflow.com/questions/135688/setting-environment-variables-in-os-x][1]

---

Coming from a Windows background where it&#39;s very easy to set and modify environment variables (just go to System Properties &gt; Advanced &gt; Environment Variables), it does not seem to be that straight forward on Mac OS 10.5. Most references say I should update /etc/profile or ~/.profile. Are those the equivalent of System Variables and User Variables? For example, where should I set my `JAVA_HOME` variable?


---

EDIT:

I want to be able to access the variable from the terminal as well as an app like Eclipse. Also, I hope I don&#39;t have to restart/logout to make this take effect.


  [1]: https://stackoverflow.com/questions/135688/setting-environment-variables-in-os-x

Environment variables in Mac OS X

I&#39;d like to have access to the `$HOME` environment variable in a C++ program that I&#39;m writing. If I were writing code in C, I&#39;d just use the `getenv()` function, but I was wondering if there was a better way to do it. Here&#39;s the code that I have so far:


    std::string get_env_var( std::string const &amp; key ) {                                 
        char * val;                                                                        
        val = getenv( key.c_str() );                                                       
        std::string retval = &quot;&quot;;                                                           
        if (val != NULL) {                                                                 
            retval = val;                                                                    
        }                                                                                  
        return retval;                                                                        
    }           

Should I use `getenv()` to access environment variables in C++? Are there any problems that I&#39;m likely to run into that I can avoid with a little bit of knowledge?

Content Type	Original Author	Original Content on Stackoverflow
Question	Jesse Beder	View Question on Stackoverflow
Solution 1 - Linux	jcrossley3	View Answer on Stackoverflow
Solution 2 - Linux	dirkgently	View Answer on Stackoverflow
Solution 3 - Linux	Dagim Sisay	View Answer on Stackoverflow
Solution 4 - Linux	dimba	View Answer on Stackoverflow

How to add a default include path for GCC in Linux?

Linux Problem Overview

Linux Solutions

Solution 1 - Linux

Solution 2 - Linux

Solution 3 - Linux

Solution 4 - Linux

NSString property: copy or retain?

How do I compare two DateTime objects in PHP 5.2.8?

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