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digitalmars.D.learn - Temporary silence output (stdout)

reply "MarisaLovesUsAll" <marusya 2ch.hk> writes:
Hi!
I sometimes got a useless messages in stdout from SDL_Image
library, and I want to temporary silence it. How do I do?
May 10 2014
next sibling parent "Mark Isaacson" <turck11 hotmail.com> writes:
On Saturday, 10 May 2014 at 20:24:50 UTC, MarisaLovesUsAll wrote:

 Hi!
 I sometimes got a useless messages in stdout from SDL_Image
 library, and I want to temporary silence it. How do I do?


Consider using either version or debug statements.

If you want the messages to be opt-in, debug statements are quite
useful:
debug(myModule) writeln("Hello world!");

Which will only print when you compile with -debug=myModule

If you want more power than that, version statements can be
useful. First declare (or don't) a specific version (or several):

version = MyVersion;

Then conditionally compile code based on that:

version(MyVersion) {
    writeln("Hello World");
}

Note that the compiler declares some versions automatically, such
as version(unittest) when compiling with --unittest.
May 10 2014
prev sibling next sibling parent Artur Skawina via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:
On 05/10/14 22:24, MarisaLovesUsAll via Digitalmars-d-learn wrote:

 I sometimes got a useless messages in stdout from SDL_Image
 library, and I want to temporary silence it. How do I do?


One way would be something like:

   import std.stdio;

   void writeOutput () {
      static c = 1;
      printf("%d\n", c++);
   }

   void main() {
      writeOutput();

      {
         auto ex = PushFD!1("/dev/null".ptr);
         writeOutput();
      }

      writeOutput();
   }

   struct PushFD(int fd) {
      import core.sys.posix.fcntl, core.sys.posix.unistd;
      int old;
      this(const char* fn) { //
         old = dup(fd);
         auto nfd = open(fn, O_RDWR);
         dup2(nfd, fd);
         close(nfd);
      }
      ~this() { dup2(old, fd); close(old); }
   }

// In real code you'll want to check for errors from dup/dup2/open/close.

artur
May 10 2014
prev sibling next sibling parent "FreeSlave" <freeslave93 gmail.com> writes:
On Saturday, 10 May 2014 at 20:24:50 UTC, MarisaLovesUsAll wrote:

 Hi!
 I sometimes got a useless messages in stdout from SDL_Image
 library, and I want to temporary silence it. How do I do?


You can temporary redirect output to file. Example (on C):

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

int main ()
{
     int stdout_copy = dup(STDOUT_FILENO);

     close (STDOUT_FILENO);

     int stdout_file = creat("myfile.txt", O_RDWR); //it obtains 
the lowest free descriptor - 1, i.e. stdout.
     printf("Hello file\n");
     fflush(stdout); //don't forget to flush
     close(stdout_file);

     dup2(stdout_copy, STDOUT_FILENO);
     printf("Hello console\n");
     return 0;
}

But it's not very portable, you probably will need to write 
something other for Windows system. And there are no checks for 
errors in this example.

Also in SDL specific case it seems like it should redirect by 
default - http://sdl.beuc.net/sdl.wiki/FAQ_Console but I don't 
know whether it's true or not for SDL_Image.
May 11 2014
prev sibling parent "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:
On Saturday, 10 May 2014 at 20:24:50 UTC, MarisaLovesUsAll wrote:

 Hi!
 I sometimes got a useless messages in stdout from SDL_Image
 library, and I want to temporary silence it. How do I do?


Are you sure it's stdout, not stderr? For the latter, you would 
need to redirect FD 2, not FD 1:

     ...
     auto ex = PushFD!2("/dev/null".ptr);
     ...
May 11 2014