`...` is an extension provided by GCC

https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html#Designated-Inits

&gt; To initialize a range of elements to the same value, write `[first ...
&gt; last] = value`. This is a GNU extension. For example,
&gt; 
&gt;      int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

`&amp;&amp;` is another extension

https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels-as-Values

&gt; You can get the address of a label defined in the current function (or
&gt; a containing function) with the unary operator `&amp;&amp;`. The value has
&gt; type `void *`. This value is a constant and can be used wherever a
&gt; constant of that type is valid. For example:
&gt; 
&gt;      void *ptr;
&gt;      /* ... */
&gt;      ptr = &amp;&amp;foo;

When I click the marker on the google map, &quot;Navigation&quot; and &quot;GPS Pointer&quot; buttons come out. How can I hide those two navigation buttons programmatically in android development?

![enter image description here][1]


  [1]: http://i.stack.imgur.com/gnkkC.jpg

How to hide &quot;Navigation&quot; and &quot;GPS Pointer&quot; buttons when I click the marker on the android google map

I am using stateless spring security,but in case of signup i want to disable spring security.I disabled  using 

    antMatchers(&quot;/api/v1/signup&quot;).permitAll().

but it is not working,i am getting error below: 

     message=An Authentication object was not found in the SecurityContext, type=org.springframework.security.authentication.AuthenticationCredentialsNotFoundException

I think this means spring security filters are working

My url&#39;s order always will be &quot;/api/v1&quot;

My spring config is

    @Override
        protected void configure(HttpSecurity http) throws Exception {
    
        	 http.
             csrf().disable().
             sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS).
             and().
             authorizeRequests().
             antMatchers(&quot;/api/v1/signup&quot;).permitAll().
             anyRequest().authenticated().
             and().
             anonymous().disable();
            http.addFilterBefore(new AuthenticationFilter(authenticationManager()), BasicAuthenticationFilter.class);
        }

My authentication filter is

    @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
            HttpServletRequest httpRequest = asHttp(request);
            HttpServletResponse httpResponse = asHttp(response);
            
            String username = httpRequest.getHeader(&quot;X-Auth-Username&quot;);
            String password = httpRequest.getHeader(&quot;X-Auth-Password&quot;);
            String token = httpRequest.getHeader(&quot;X-Auth-Token&quot;);
             
            String resourcePath = new UrlPathHelper().getPathWithinApplication(httpRequest);
    
            try {
            	
                if (postToAuthenticate(httpRequest, resourcePath)) {            
                    processUsernamePasswordAuthentication(httpResponse, username, password);
                    return;
                }
                
                if(token != null){
                	processTokenAuthentication(token);
                }
                chain.doFilter(request, response);
            } catch (InternalAuthenticationServiceException internalAuthenticationServiceException) {
                SecurityContextHolder.clearContext();
                logger.error(&quot;Internal authentication service exception&quot;, internalAuthenticationServiceException);
                httpResponse.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            } catch (AuthenticationException authenticationException) {
                SecurityContextHolder.clearContext();
                httpResponse.sendError(HttpServletResponse.SC_UNAUTHORIZED, authenticationException.getMessage());
            } finally {
            }
        }
    	
    	 private HttpServletRequest asHttp(ServletRequest request) {
    	        return (HttpServletRequest) request;
    	    }
    
    	    private HttpServletResponse asHttp(ServletResponse response) {
    	        return (HttpServletResponse) response;
    	    }
    	    
    	    private boolean postToAuthenticate(HttpServletRequest httpRequest, String resourcePath) {
    	        return Constant.AUTHENTICATE_URL.equalsIgnoreCase(resourcePath) &amp;&amp; httpRequest.getMethod().equals(&quot;POST&quot;);
    	    }
    
    	    private void processUsernamePasswordAuthentication(HttpServletResponse httpResponse,String username, String password) throws IOException {
    	        Authentication resultOfAuthentication = tryToAuthenticateWithUsernameAndPassword(username, password);
    	        SecurityContextHolder.getContext().setAuthentication(resultOfAuthentication);
    	        httpResponse.setStatus(HttpServletResponse.SC_OK);
    	        httpResponse.addHeader(&quot;Content-Type&quot;, &quot;application/json&quot;);
    	        httpResponse.addHeader(&quot;X-Auth-Token&quot;, resultOfAuthentication.getDetails().toString());
    	    }
    
    	    private Authentication tryToAuthenticateWithUsernameAndPassword(String username,String password) {
    	        UsernamePasswordAuthenticationToken requestAuthentication = new UsernamePasswordAuthenticationToken(username, password);
    	        return tryToAuthenticate(requestAuthentication);
    	    }
    	    
    	    private void processTokenAuthentication(String token) {
    	        Authentication resultOfAuthentication = tryToAuthenticateWithToken(token);
    	        SecurityContextHolder.getContext().setAuthentication(resultOfAuthentication);
    	    }
    	    
    	    private Authentication tryToAuthenticateWithToken(String token) {
    	        PreAuthenticatedAuthenticationToken requestAuthentication = new PreAuthenticatedAuthenticationToken(token, null);
    	        return tryToAuthenticate(requestAuthentication);
    	    }
    
    	    private Authentication tryToAuthenticate(Authentication requestAuthentication) {
    	        Authentication responseAuthentication = authenticationManager.authenticate(requestAuthentication);
    	        if (responseAuthentication == null || !responseAuthentication.isAuthenticated()) {
    	            throw new InternalAuthenticationServiceException(&quot;Unable to authenticate Domain User for provided credentials&quot;);
    	        }
    	        logger.debug(&quot;User successfully authenticated&quot;);
    	        return responseAuthentication;
    	    }

My controller is 

    @RestController
    public class UserController {
    	
    	@Autowired
    	UserService userService;
    
    	/**
    	 * to pass user info to service
    	 */
    	@RequestMapping(value = &quot;api/v1/signup&quot;,method = RequestMethod.POST)
    	public String saveUser(@RequestBody User user) {
    		userService.saveUser(user);
    		return &quot;User registerted successfully&quot;;
    	}
    }

I am totally new to spring,please help me how to do it ?

How to disable spring security for particular url

Refering to [js0n.c][1]

The code syntax is as below:

        static void *gostruct[] =
        {
        	[0 ... 255] = &amp;&amp;l_bad,
        	[&#39;\t&#39;] = &amp;&amp;l_loop, [&#39; &#39;] = &amp;&amp;l_loop, [&#39;\r&#39;] = &amp;&amp;l_loop, [&#39;\n&#39;] = &amp;&amp;l_loop,
        	[&#39;&quot;&#39;] = &amp;&amp;l_qup,
        	[&#39;:&#39;] = &amp;&amp;l_loop, [&#39;,&#39;] = &amp;&amp;l_loop,
        	[&#39;[&#39;] = &amp;&amp;l_up, [&#39;]&#39;] = &amp;&amp;l_down, // tracking [] and {} individually would allow fuller validation but is really messy
        	[&#39;{&#39;] = &amp;&amp;l_up, [&#39;}&#39;] = &amp;&amp;l_down,
        	[&#39;-&#39;] = &amp;&amp;l_bare, [48 ... 57] = &amp;&amp;l_bare, // 0-9
        	[65 ... 90] = &amp;&amp;l_bare, // A-Z
        	[97 ... 122] = &amp;&amp;l_bare // a-z
        };
    
    ........
    .......
    
    l_bad:
    	*vlen = cur - json; // where error&#39;d
        return 0;
    
    ........
    ........

Can anyone explain what is being done here? What does syntax `[0 ... 255]` and 
`&amp;&amp;l_bad` do here?

  [1]: https://github.com/quartzjer/js0n

What is this &quot;[0 ... 255] =&quot; syntax in C?

Refering to <a href="https://github.com/quartzjer/js0n" target="_blank" rel="noopener noreferrer">js0n.c</a>
The code syntax is as below:
<pre><code class="hljs language-scss"> static void *gostruct[] =
 {
 	[0 ... 255] = &#x26;&#x26;l_bad,
 	['\t'] = &#x26;&#x26;l_loop, [' '] = &#x26;&#x26;l_loop, ['\r'] = &#x26;&#x26;l_loop, ['\n'] = &#x26;&#x26;l_loop,
 	['"'] = &#x26;&#x26;l_qup,
 	[':'] = &#x26;&#x26;l_loop, [','] = &#x26;&#x26;l_loop,
 	['['] = &#x26;&#x26;l_up, [']'] = &#x26;&#x26;l_down, // tracking [] and {} individually would allow fuller validation but is really messy
 	['{'] = &#x26;&#x26;l_up, ['}'] = &#x26;&#x26;l_down,
 	['-'] = &#x26;&#x26;l_bare, [48 ... 57] = &#x26;&#x26;l_bare, // 0-9
 	[65 ... 90] = &#x26;&#x26;l_bare, // A-Z
 	[97 ... 122] = &#x26;&#x26;l_bare // a-z
 };

........
.......

l_bad:
	*vlen = cur - json; // where error'd
 return 0;

........
........
</code></pre>
Can anyone explain what is being done here? What does syntax <code>[0 ... 255]</code> and
<code>&#x26;&#x26;l_bad</code> do here?

If `buf` is a `malloc()` allocated char buffer, does `free(buf)` set/reset `errno`?

Let&#39;s say I want to write the buffer to a file, and then free it, as I don&#39;t need it any more.

Let&#39;s say the error policy for the code is to return -1 on an error. 

Is this a proper way to write out the buffer and error check without leaking memory?

    fputs(buf, somefile);
    free(buf);
    if (errno) return -1;

Or do I need to consider free possibly setting errno, as in...

    fputs(buf, somefile);
    if (errno){ 
        free(buf);
        return -1;
    }
    free(buf);

or, horror of horrors, 

    do { 
      fputs(buf, somefile);
      int save_errno = errno;
      free(buf);
      errno = save_errno;
      if (errno) return -1;
    } while(0);  
    
where the use of a block allows for a local save_errno to exist in various places should this need to be reused.  

All of this would seem to depend on whether free() sets errno.  

The [linux man page for free()](http://linux.die.net/man/3/free) is also the man page for `malloc()`, etc.  It mentions `malloc()` setting errno, but not `free()`. 

The [GNU C Library manual page for freeing dynamic memory](http://www.gnu.org/software/libc/manual/html_node/Freeing-after-Malloc.html#Freeing-after-Malloc) does not mention whether free() sets errno. 

So I wrote a short program to force a write error so I could see if free() reset errno, and it does not.  I&#39;m wondering if I should rely upon this result and the fact that free() is so essential that &quot;of course it doesn&#39;t set errno.&quot;  

    # See if free() resets errno on a bad write
    #include &lt;errno.h&gt;
    #include &lt;stdio.h&gt;
    #include &lt;stdlib.h&gt;
    #include &lt;string.h&gt;
    
    int main(int argc, char **argv)
    {
      char * buf = malloc(256);
      snprintf(buf,256,&quot;%s\n&quot;, &quot;Hello, World!&quot;);
    
      FILE *badfile;
    
      badfile = fopen(&quot;/dev/null&quot;,&quot;r&quot;);
   
      fputs(buf, badfile);
      free(buf);
      printf(&quot;%d\n&quot;, errno);
      printf(&quot;%s\n&quot;, strerror(errno));
    }



Does free() set errno?

After reading [this answer][2] about undefined behavior and sequence points, I wrote a small program:

    #include &lt;stdio.h&gt;

    int main(void) {
      int i = 5;
      i = (i, ++i, 1) + 1;
      printf(&quot;%d\n&quot;, i);
      return 0;
    }

The output is `2`. Oh God, I didn&#39;t see the decrement coming! What is happening here?

Also, while compiling the above code, I got a warning saying:

&gt; px.c:5:8: warning: left-hand operand of comma expression has no effect&lt;br&gt;
&gt;
&gt;       [-Wunused-value]   i = (i, ++i, 1) + 1;
&gt;                             ^

Why? But probably it will be automatically answered by the answer of my first question.

  [1]: https://stackoverflow.com/questions/30605380/bash-usr-bin-hydra-pmi-proxy-no-such-file-or-directory
  [2]: https://stackoverflow.com/a/4176333/2411320


What does i = (i, ++i, 1) + 1; do?

Here is my code:

    #include &lt;stdio.h&gt;
    #include &lt;string.h&gt;
    #include &lt;stdlib.h&gt;
    #include &lt;netdb.h&gt;
    #include &lt;sys/types.h&gt;
    #include &lt;sys/socket.h&gt;
    #include &lt;arpa/inet.h&gt;
    
    int main (void) {
      
      struct addrinfo hints; 
      memset (&amp;hints, 0, sizeof hints);
      
      hints.ai_family = AF_UNSPEC; 
      hints.ai_socktype = SOCK_DGRAM;  
      hints.ai_flags = AI_CANONNAME;   
      
      struct addrinfo *res;
    
      getaddrinfo (&quot;example.com&quot;, &quot;http&quot;, &amp;hints, &amp;res);
      printf (&quot;Host: %s\n&quot;, &quot;example.com&quot;);
      
      void *ptr;
    
      while (res != NULL) {
        printf(&quot;AI Family for current addrinfo: %i\n&quot;, res-&gt;ai_family);
        switch (res-&gt;ai_family) {
          case AF_INET:
            ptr = (struct sockaddr_in *) res-&gt;ai_addr;
            struct sockaddr_in *sockAddrIn = (struct sockaddr_in *) res-&gt;ai_addr;
            break;
        }
        res = res-&gt;ai_next;
      }
      return 0;
    }

which compiles fine.

However when I comment out this line:

    //ptr = (struct sockaddr_in *) res-&gt;ai_addr;

I will get:

    $ gcc ex4.c
    ex4.c:30:9: error: expected expression
            struct sockaddr_in *sockAddrIn = (struct sockaddr_in *) res-&gt;ai_addr;
            ^
    1 error generated.

What am I missing? 

Switch-case won&#39;t compile after commenting out an unused line

I observed that `rand()` library function when it is called just once within a loop, it almost always produces positive numbers.

    for (i = 0; i &lt; 100; i++) {
        printf(&quot;%d\n&quot;, rand());
    }

But when I add two `rand()` calls, the numbers generated now have more negative numbers.

    for (i = 0; i &lt; 100; i++) {
        printf(&quot;%d = %d\n&quot;, rand(), (rand() + rand()));
    }

Can someone explain why I am seeing negative numbers in the second case?

PS: I initialize the seed before the loop as `srand(time(NULL))`.

Why does rand() + rand() produce negative numbers?

A struct can be either passed/returned by value or passed/returned by reference (via a pointer) in C.

The general consensus seems to be that the former can be applied to small structs without penalty in most cases. See [Is there any case for which returning a structure directly is good practice?](https://stackoverflow.com/a/7550578) and [Are there any downsides to passing structs by value in C, rather than passing a pointer?](https://stackoverflow.com/a/161845/5036089)

And that avoiding a dereference can be beneficial from both a speed and clarity perspective. But what counts as *small*? I think we can all agree that this is a small struct:

    struct Point { int x, y; };

That we can pass by value with relative impunity:

    struct Point sum(struct Point a, struct Point b) {
      return struct Point { .x = a.x + b.x, .y = a.y + b.y };
    }

And that Linux&#39;s `task_struct` is a large struct:

https://github.com/torvalds/linux/blob/b953c0d234bc72e8489d3bf51a276c5c4ec85345/include/linux/sched.h#L1292-1727

That we&#39;d want to avoid putting on the stack at all costs (especially with those 8K kernel mode stacks!). But what&#39;s about middling ones? I assume structs smaller than a register are fine. But what about these?

    typedef struct _mx_node_t mx_node_t;
    typedef struct _mx_edge_t mx_edge_t;

    struct _mx_edge_t {
      char symbol;
      size_t next;
    };

    struct _mx_node_t {
      size_t id;
      mx_edge_t edge[2];
      int action;
    };

What is the best **rule of thumb** for determining whether a struct is small enough that it&#39;s safe to pass it around by value (short of extenuating circumstances such as some deep recursion)?

Lastly please don&#39;t tell me that I need to profile. I&#39;m asking for a heuristic to use when I&#39;m too lazy/it&#39;s not worth it to investigate further.

EDIT: I have two followup questions based on the answers so far:

1. What if the struct is actually *smaller* than a pointer to it?

2. What if a shallow copy is the desired behavior (the called function will perform a shallow copy anyway)?

EDIT: Not sure why this got marked as a possible duplicate as I actually link the other question in my question. I&#39;m asking for clarification on what constitutes a *small* struct and am well aware that most of the time structs should be passed by reference.

Content Type	Original Author	Original Content on Stackoverflow
Question	Gaurav K	View Question on Stackoverflow
Solution 1 - C	user657267	View Answer on Stackoverflow

What is this "[0 ... 255] =" syntax in C?

C Problem Overview

C Solutions

Solution 1 - C

How to disable spring security for particular url

How to hide "Navigation" and "GPS Pointer" buttons when I click the marker on the android google map

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