Differences betwen al_ustr_new and al_ustr_new()

no-reply@allegro.cc (AMCerasoli) — Mon, 26 Sep 2011 05:00:27 +0000

Hi there!.

Who is kind enough to give me an explanation about the differences between al_ustr_new_from_buffer() and al_ustr_new(). Obviously a technical explanation, since have just save me a lot of trouble, I was getting a lot of garbage from one of my char pointers when reading from file an using the al_ustr_new_from_buffer() function the problem have just disappeared... It's like eliminates the garbage automatically. But that garbage seems to be created by the al_fread function.

Thanks.

PS: I know I could search in the source, but I doubt I could understand something...

DAMN!! THE TITTLE! fuck!

no-reply@allegro.cc (Matthew Leverton) — Mon, 26 Sep 2011 05:15:59 +0000

al_ustr_new(s) is the same thing as al_ustr_new_from_buffer(s, strlen(s)).

no-reply@allegro.cc (AMCerasoli) — Mon, 26 Sep 2011 06:49:03 +0000

Well... On my system they don't return the same result.

al_ustr_new() gives me a lot of garbage and al_ustr_new_from_buffer() works fine, this is the smaller example I could come up with. Probable I'm doing something wrong.

Check out the console, not the allegro window.

#SelectExpand
   1#include 
   2#include 
   3#include 
   4#include 
   5
   6class OPC_DATA{
   7
   8  public:
   9
  10     bool modalidad_normal;
  11     bool catg0, catg1, catg2, catg3, catg4;
  12     ALLEGRO_USTR* URL_page;
  13     float sfx, music;
  14     bool fullscreen;
  15     int len;
  16
  17
  18     OPC_DATA() {
  19
  20        ALLEGRO_FILE* file = al_fopen("datos.dat", "rb");
  21
  22        if(file){ ///Si el archivo existe...
  23
  24           modalidad_normal = al_fread32be(file);
  25           catg0            = al_fread32be(file);
  26           catg1            = al_fread32be(file);
  27           catg2            = al_fread32be(file);
  28           catg3            = al_fread32be(file);
  29           catg4            = al_fread32be(file);
  30           len              = al_fread32be(file);
  31
  32           std::cout<<"len: "<<len<<std::endl;
  33           if(len==5)Beep(600,20);
  34
  35           char *buf = new char [len];
  36           al_fread(file, buf, len);
  37
  38           if(len==0) // This is because if the len==0 the URL_page variable is filled with garbage
  39              URL_page = al_ustr_new("");
  40           else
  41              ///Here!! <<<---- Change the functions a see the difference.
  42              ///               remember to delete the datos.dat file after changing the function
  43              //URL_page = al_ustr_new(buf); //This is bad
  44              URL_page = al_ustr_new_from_buffer(buf, len);  // This is good
  45
  46           delete [] buf;
  47
  48           int T_sfx        = al_fread32be(file);
  49           sfx   = *reinterpret_cast<float*>(&T_sfx);
  50
  51           int T_music      = al_fread32be(file);
  52           music = *reinterpret_cast<float*>(&T_music);
  53
  54           fullscreen       = al_fread32be(file);
  55
  56           al_fclose(file);
  57           //Beep(800,200);
  58
  59        }else{ /// Si el archivo NO existe...
  60
  61           modalidad_normal = true;
  62           catg0            = true;
  63           catg1            = true;
  64           catg2            = true;
  65           catg3            = true;
  66           catg4            = true;
  67           URL_page = al_ustr_new("");
  68           sfx              = 1.6;
  69           music            = 1.5;
  70           fullscreen       = false;
  71
  72           al_fclose(file);
  73        }
  74
  75     }
  76
  77     ~OPC_DATA() {
  78
  79        ALLEGRO_FILE* file = al_fopen("datos.dat", "wb");
  80
  81        al_fwrite32be(file, modalidad_normal);
  82        al_fwrite32be(file, catg0);
  83        al_fwrite32be(file, catg1);
  84        al_fwrite32be(file, catg2);
  85        al_fwrite32be(file, catg3);
  86        al_fwrite32be(file, catg4);
  87
  88        al_fwrite32be(file, (int)al_ustr_size(URL_page));
  89        al_fwrite(file, al_cstr(URL_page), al_ustr_size(URL_page));
  90
  91        al_fwrite32be(file, *reinterpret_cast<int*>(&sfx));
  92        al_fwrite32be(file, *reinterpret_cast<int*>(&music));
  93        al_fwrite32be(file, fullscreen);
  94
  95        al_fclose(file);
  96        al_ustr_free(URL_page);
  97
  98     }
  99
 100};
 101
 102int main()
 103{
 104    al_init();
 105
 106    al_init_font_addon(); // initialize the font addon
 107    al_init_ttf_addon();// initialize the ttf (True Type Font) addon
 108    ALLEGRO_FONT *font = al_load_ttf_font("consola.ttf",72,0 ); // load the font | Font from Larabie Free Fonts
 109    ALLEGRO_DISPLAY *display = NULL;
 110    display = al_create_display(640,480);
 111
 112// Closing and opening simulation
 113
 114    for (int i=0;i<5;i++){
 115       OPC_DATA *od = new OPC_DATA;
 116       al_ustr_append_chr(od->URL_page, 97); // This adds the letter "a"
 117       delete od;
 118    }
 119// - - - - - - - - - - - - - - - -
 120
 121    OPC_DATA *od1 = new OPC_DATA;
 122    al_ustr_append_chr(od1->URL_page, 97);
 123
 124    al_clear_to_color(al_map_rgb(50,10,70));
 125    al_draw_ustr(font, al_map_rgb(255,255,255), 640/2, (480/4),ALLEGRO_ALIGN_CENTRE, od1->URL_page);
 126
 127    al_flip_display();
 128
 129    std::cout<<al_cstr(od1->URL_page);
 130    al_rest(0.9);
 131
 132    al_destroy_display(display);
 133    delete od1;
 134
 135    return 0;
 136}

no-reply@allegro.cc (SiegeLord) — Mon, 26 Sep 2011 06:58:13 +0000

Well, as Matthew said, al_ustr_new uses strlen which computes the length of the string by looking for the first 0 character in that memory block. I'd guess that you don't write the trailing 0 when you save the .dat file, so strlen reports something much larger than what it should be.

no-reply@allegro.cc (Matthew Leverton) — Mon, 26 Sep 2011 06:59:58 +0000

Change it to:

char *buf = new char [len + 1];
buf[len] = 0;

You must null terminate each of your strings. (Or you can use al_ustr_new_from_buffer() for every case.)

no-reply@allegro.cc (SiegeLord) — Mon, 26 Sep 2011 07:07:44 +0000

~~That won't help though since~~ he does this (confirming my guess):

#SelectExpand
 89al_fwrite(file, al_cstr(URL_page), al_ustr_size(URL_page));

And al_ustr_size doesn't include the trailing 0.

Just use the al_ustr_new_from_buffer and be done with it.

EDIT: Nvm, can't read.

no-reply@allegro.cc (Matthew Leverton) — Mon, 26 Sep 2011 07:11:13 +0000

SiegeLord said:

That won't help though since he does this (confirming my guess):

I'm talking about when he loads the strings.

But I'd use al_ustr_new_from_buffer() since it exists for this purpose.

no-reply@allegro.cc (AMCerasoli) — Mon, 26 Sep 2011 14:29:11 +0000

Hmm, I get it now, I didn't know that al_ustr_new() was looking for the null character, but otherwise how would know when to stop?.

Yhea the best choice is to keep using al_ustr_new_from_buffer() since I'm already saving a flag into the file, otherwise I could save the string with the null character included, and read the file until I find that null charter and then move on with the rest, and I wouldn't need the len flag.