These lines are hints for debugging (where the code following the line actually came from)

    # line-number &quot;source-file&quot; [flags]

Meaning of flags (space separated):

 - 1 - Start of a new file
 - 2 - Returning to previous file
 - 3 - Following text comes from a system header file (#include &lt;&gt; vs #include &quot;&quot;)
 - 4 - Following text should be treated as being wrapped in an implicit extern &quot;C&quot; block.

These *linemarkers* are mentioned in `man gcc` for `-P` option.

The `-P` option is specifically meant to get rid of these lines for clarity:

    gcc -E -P source.c

See [detailed documentation][1] (answered before).


  [1]: https://gcc.gnu.org/onlinedocs/cpp/Preprocessor-Output.html

Those are line synchronization directives, which allow `gcc` to give correct error messages for errors in `#include`d files.  Other preprocessors (such as `yacc`/`bison`) use the same mechanism to relate C errors to the correct lines in the input `.y` file.

Where can I get a list of easily parseable country codes and names? Note: 2 letter codes wanted. Examples:

au,Australia

uk,United Kingdom

us,United States

etc



Csv list of country codes/names?

I have a c# win app program. I save the text with html format in my database but I want to show it in a webbrowser to my user.How to display the string html contents into webbrowser control?

thanks in advance

How to display the string html contents into webbrowser control?

I print out the output of C preprocessor by using

    gcc -E a.c
The output contains many lines like

    # 1 &quot;a.c&quot;
    # 1 &quot;&lt;built-in&gt;&quot;
    # 1 &quot;&lt;command-line&gt;&quot;
    # 1 &quot;a.c&quot;
    # 1 &quot;c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/stdio.h&quot; 1 3
    # 19 &quot;c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/stdio.h&quot; 3
    # 1 &quot;c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/_mingw.h&quot; 1 3
    # 31 &quot;c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/_mingw.h&quot; 3
           
    # 32 &quot;c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/_mingw.h&quot; 3
    # 20 &quot;c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/stdio.h&quot; 2 3

I&#39;ve never seen this kind of syntax in C. Can someone explain what this is doing?

What is the meaning of lines starting with a hash sign and number like &#39;# 1 &quot;a.c&quot;&#39; in the gcc preprocessor output?

I print out the output of C preprocessor by using
<pre><code class="hljs language-css">gcc -E a.c
</code></pre>
The output contains many lines like
<pre><code class="hljs language-swift"># 1 "a.c"
# 1 "&#x3C;built-in>"
# 1 "&#x3C;command-line>"
# 1 "a.c"
# 1 "c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/stdio.h" 1 3
# 19 "c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/stdio.h" 3
# 1 "c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/_mingw.h" 1 3
# 31 "c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/_mingw.h" 3
 
# 32 "c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/_mingw.h" 3
# 20 "c:\\mingw\\bin\\../lib/gcc/mingw32/4.5.0/../../../../include/stdio.h" 2 3
</code></pre>
I've never seen this kind of syntax in C. Can someone explain what this is doing?

I recently encountered some code that gcc would not compile without this arg. I checked the gcc man page, but did not find this specific option. I did find `XOPEN_SOURCE`, but there was little explanation of what it does.

Can someone please elaborate? I know `-D_XOPEN_SOURCE` can be set to different values, such `400`, `600`, but what do those do?

What does -D_XOPEN_SOURCE do/mean?

I am trying to understand how can I make my program a daemon.So some things which I came across are In general, a program performs the following steps to become a daemon:  

1. Call `fork( )`. 
2. In the parent, call `exit( )`. This ensures that the original parent (the daemon&#39;s
grandparent) is satisfied that its child terminated, that the daemon&#39;s parent is no
longer running, and that the daemon is not a process group leader. This last point
is a requirement for the successful completion of the next step.  

3. Call `setsid( )`, giving the daemon a new process group and session, both of
  which have it as leader. This also ensures that the process has no associated
  controlling terminal (as the process just created a new session, and will not assign
  one).

4. Change the working directory to the root directory via `chdir( )`. This is done
because the inherited working directory can be anywhere on the filesystem.
Daemons tend to run for the duration of the system&#39;s uptime, and you don&#39;t want
to keep some random directory open, and thus prevent an administrator from
unmounting the filesystem containing that directory.

5. Close all file descriptors. 
6. Open file descriptors 0, 1, and 2 (standard in, standard out, and standard error)
and redirect them to `/dev/null`.


&lt;pre&gt;&lt;code&gt;#include &amp;lt;sys/types.h&amp;gt;
#include &amp;lt;sys/stat.h&amp;gt;
#include &amp;lt;stdlib.h&amp;gt;
#include &amp;lt;stdio.h&amp;gt;
#include &amp;lt;fcntl.h&amp;gt;
#include &amp;lt;unistd.h&amp;gt;
#include &amp;lt;linux/fs.h&amp;gt;

int main (void)
{
    pid_t pid;
    int i;
    
    /* create new process */
    pid = fork ( );  
    if (pid == -1)  
        return -1;  
    else if (pid != 0)  
        exit (EXIT_SUCCESS);  

    /* create new session and process group */  
    if (setsid ( ) == -1)  
        return -1;  

    /* set the working directory to the root directory */  
    if (chdir (&quot;/&quot;) == -1)  
        return -1;  

    /* close all open files--NR_OPEN is overkill, but works */  
    for (i = 0; i &amp;lt; NR_OPEN; i++)  
        close (i);  

    /* redirect fd&#39;s 0,1,2 to /dev/null */  
    open (&quot;/dev/null&quot;, O_RDWR);  
    /* stdin */  
    dup (0);  
    /* stdout */  
    dup (0);  
    /* stderror */  
    
    /* do its daemon thing... */  
    
    return 0;  
}&lt;/code&gt;&lt;/pre&gt;  



Can some one give me a link to existing source code of some program like Apache so that I can understand this process in more depth.


how to make a process daemon

I&#39;m a little bit confused about something. I was under the impression that the correct way of reading a C string with `scanf()` went along the lines of

(never mind the possible buffer overflow, it&#39;s just a simple example)

    char string[256];
    scanf( &quot;%s&quot; , string );

However, the following seems to work too,

    scanf( &quot;%s&quot; , &amp;string );

Is this just my compiler (gcc), pure luck, or something else?

Why does reading into a string buffer with scanf work both with and without the ampersand (&amp;)?

there has been many previous questions about redirecting  stdout/stderr to a file. is there a way to redirect  stdout/stderr to a string?

redirect stdout/stderr to a string

I&#39;ve been trying to figure out how the fork-exec mechanism is used inside Linux.  Everything was going on according to the plan until some web pages started to confuse me.

It is said that a child process should strictly use `_exit()` instead of a simple `exit()` or a normal return from `main()`. 

As I know, Linux shell fork-execs every one of the external commands; assuming what I said above is true, the conclusion is that none of these external commands nor any other execution happening inside the Linux shell can do normal return!

Wikipedia &amp; some other webpages claim we&#39;ve got to use `_exit()` just to prevent a child process causing deletion of parent&#39;s temporary files while a probable double flushing of stdio buffers may happen. though I understand the former, I have no clues how a double flushing of buffers could be harmful to a Linux system.

I&#39;ve spent my whole day on this...
Thanks for any clarification.

What is the difference between using _exit() &amp; exit() in a conventional Linux fork-exec?

I ran into an interesting issue today.  Consider this simple example:

    template &lt;typename T&gt;
    void foo(const T &amp; a) { /* code */ }

    // This would also fail
    // void foo(const int &amp; a) { /* code */ }
    
    class Bar
    {
    public:
       static const int kConst = 1;
       void func()
       {
          foo(kConst);           // This is the important line
       }
    };
    
    int main()
    {
       Bar b;
       b.func();
    }

When compiling I get an error:

    Undefined reference to &#39;Bar::kConst&#39;

Now, I&#39;m pretty sure that this is because the `static const int` is not defined anywhere, which is intentional because according to my understanding the compiler should be able to make the replacement at compile-time and not need a definition.  However, since the function takes a `const int &amp;` parameter, it seems to be not making the substitution, and instead preferring a reference.  I can resolve this issue by making the following change:

    foo(static_cast&lt;int&gt;(kConst));

I believe this is now forcing the compiler to make a temporary int, and then pass a reference to that, which it can successfully do at compile time.

I was wondering if this was intentional, or am I expecting too much from gcc to be able to handle this case?  Or is this something I shouldn&#39;t be doing for some reason?

Undefined reference to static const int

I know there is something like `find_package(Threads)` but it doesn&#39;t seem to make a difference (at least by itself). For now I&#39;m using `SET(CMAKE_C_FLAGS ${CMAKE_C_FLAGS} &quot;-pthread&quot;)`, but it doesn&#39;t look like a correct solution to me.


How do I force cmake to include &quot;-pthread&quot; option during compilation?

I&#39;m compiling my C++ app using GCC 4.3. Instead of manually selecting the optimization flags I&#39;m using `-march=native`, which in theory should add all optimization flags applicable to the hardware I&#39;m compiling on. But how can I check which flags is it actually using?

How to see which flags -march=native will activate?

I need to specialize template member function for some type (let&#39;s say **double**). It works fine while class `X` itself is not a template class, but when I make it template GCC starts giving compile-time errors.

    #include &lt;iostream&gt;
    #include &lt;cmath&gt;
    
    template &lt;class C&gt; class X
    {
    public:
       template &lt;class T&gt; void get_as();
    };
    
    template &lt;class C&gt;
    void X&lt;C&gt;::get_as&lt;double&gt;()
    {
    
    }
    
    int main()
    {
       X&lt;int&gt; x;
       x.get_as();
    }

here is the error message

    source.cpp:11:27: error: template-id
      &#39;get_as&lt;double&gt;&#39; in declaration of primary template
    source.cpp:11:6: error: prototype for
      &#39;void X&lt;C&gt;::get_as()&#39; does not match any in class &#39;X&lt;C&gt;&#39;
    source.cpp:7:35: error: candidate is:
      template&lt;class C&gt; template&lt;class T&gt; void X::get_as()

How can I fix that and what is the problem here?

Thanks in advance.

explicit specialization of template class member function

I&#39;m trying to figure out how I can concatenate a `#define`&#39;d int to a `#define`&#39;d string using the **C** Preprocessor.  My compiler is GCC 4.1 on CentOS 5.  The solution should also work for MinGW.

I&#39;d like to append a version number onto a string, but the only way I can get it to work is to make a copy of the version number defines as strings.

The closest thing I could find was a method of quoting macro arguments, but it doesn&#39;t work for `#define`s

This is does not work.

    #define MAJOR_VER 2
    #define MINOR_VER 6
    #define MY_FILE &quot;/home/user/.myapp&quot; #MAJOR_VER #MINOR_VER

It doesn&#39;t work without the `#`s either because the values are numbers and it would expand to `&quot;/home/user/.myapp&quot; 2 6`, which isn&#39;t valid **C**.

This does work, but I don&#39;t like having copies of the version defines because I do need them as numbers as well.

    #define MAJOR_VER 2
    #define MINOR_VER 6
    #define MAJOR_VER_STR &quot;2&quot;
    #define MINOR_VER_STR &quot;6&quot;
    #define MY_FILE &quot;/home/user/.myapp&quot; MAJOR_VER_STRING MINOR_VER_STRING



Concatenate int to string using C Preprocessor

This question has evolved over the past several weeks to cover more general issues with [tag:xcode4] (and upgrading projects form older [tag:xcode]s).

However many of the issues can be solved by following the same set of instructions.

If you have any of the following issues, try the methods in the accepted answer:

- Xcode 4 fails to archive an App
- Xcode 4 creates an unusable archive
- Xcode 4 does not create an .ipa
- Xcode 4 fails to compile due to preprocessor errors
- Xcode 4 cannot find headers
- Xcode 4&#39;s code complete is not working
- Project dependancies won&#39;t compile
- Adding a dependancy causes any of the above issues

## Original Question
Title: *&quot;lexical or preprocessor issue file not found&quot; in Xcode 4*

I have a project in Xcode 4 that will build fine and run on the device and simulator but when trying to Archive it errors when looking for headers files associated with a static library:

    In file included from /Volumes/Development/Path/LBProject/LBProject/LBProject-Prefix.pch:15:
    In file included from /Volumes/Development/Path/LBProject/LBFDefines.h:23:
    In file included from /Volumes/Development/Path/LBProject/Classes/LBProjectAppDelegate.h:11:
    In file included from /Volumes/Development/Path/LBProject/LBProject/../FKNDirectory/FKNDirectoryManager.h:10:
    /Volumes/Development/Path/LBProject/LBProject/../FKNDirectory/FKNDataModel.h:11:9: fatal error: &#39;Merchant.h&#39; file not found [1]
     #import &quot;Merchant.h&quot;
             ^
    1 error generated. 

Xcode gives the error

    lexical or preprocessor issue file not found 

*Much* Googling has show many people are having this issue but no solution. Anyone got a fix or even a clue. 

**Update:** The `user header` search paths are set to `${BUILT_PRODUCTS_DIR}` in all configurations. It builds fine using any configuration except when archiving. 

**Update 2:** `Merchant.h` is a Core Data class that is auto-generated and therefore inside `.xcdatamodeld` package, however the headers are all copied to the public headers directory when the library is built.

Compile, Build or Archive problems with Xcode 4 (and dependencies)

I am trying to write something like this:

    #define COV_ON(x) \
                    #ifdef COVERAGE_TOOL \
                        _Pragma (COVERAGE #x)
                    #endif

Is there any way to define `COV_ON` like this? I know what I have done above is wrong as I can&#39;t have `#ifdef` inside #define. (`#` is not an allowed character in `#define`). 
So is there any solution?

#ifdef inside #define

There is a [well-known][1] [problem][2] with empty args for variadic macros in C99.

example:

    #define FOO(...)       printf(__VA_ARGS__)
    #define BAR(fmt, ...)  printf(fmt, __VA_ARGS__)

    FOO(&quot;this works fine&quot;);
    BAR(&quot;this breaks!&quot;);

The use of `BAR()` above is indeed incorrect according to the C99 standard, since it will expand to:

    printf(&quot;this breaks!&quot;,);

Note the trailing comma - not workable.

Some compilers (eg: Visual Studio 2010) will quietly get rid of that trailing comma for you. Other compilers (eg: GCC) support putting `##` in front of `__VA_ARGS__`, like so:

    #define BAR(fmt, ...)  printf(fmt, ##__VA_ARGS__)

But is there a standards-compliant way to get this behavior?
Perhaps using multiple macros?

Right now, the `##` version seems fairly well-supported (at least on my platforms), but I&#39;d really rather use a standards-compliant solution.

Pre-emptive: I know I could just write a small function. I&#39;m trying to do this using macros.

__Edit__: Here is an example (though simple) of why I would want to use BAR():

    #define BAR(fmt, ...)  printf(fmt &quot;\n&quot;, ##__VA_ARGS__)
    
    BAR(&quot;here is a log message&quot;);
    BAR(&quot;here is a log message with a param: %d&quot;, 42);

This automatically adds a newline to my BAR() logging statements, assuming `fmt` is always a double-quoted C-string. It does NOT print the newline as a separate printf(), which is advantageous if the logging is line-buffered and coming from multiple sources asynchronously.



  [1]: https://stackoverflow.com/questions/4054085/gcc-appending-to-va-args
  [2]: http://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html

Standard alternative to GCC&#39;s ##__VA_ARGS__ trick?

So I can do something like

    #ifdef MSVC
    //do compiler specific code here
    #endif

Content Type	Original Author	Original Content on Stackoverflow
Question	user607722	View Question on Stackoverflow
Solution 1 - C	jdehaan	View Answer on Stackoverflow
Solution 2 - C	uvsmtid	View Answer on Stackoverflow
Solution 3 - C	geekosaur	View Answer on Stackoverflow

What is the meaning of lines starting with a hash sign and number like '# 1 "a.c"' in the gcc preprocessor output?

C Problem Overview

C Solutions

Solution 1 - C

Solution 2 - C

Solution 3 - C

How to display the string html contents into webbrowser control?

Csv list of country codes/names?

Attributions