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(OS: Windows 7, Compiler: Visual Studio 2010 C++ compiler)

I've got a correctly working OpenGL program that draws some spheres and models, applies some shaders etc.. etc..

Now I thought it would be nice to add some text, so I added the following three lines to my draw method:

glColor3f(0.5f, 0.5f, 0.5f);
glRasterPos2f(0, 0);
glutBitmapString(GLUT_BITMAP_HELVETICA_12, (unsigned char*)"some text");

Now somehow this all makes my program get stuck in an infinite "access violation" loop, which I can't seem to fix. I even commented all the other draw code out, to just output the text, and it still gives the access violation error, I'm at a loss here because there is nothing that seems to affect this. So does anybody have some pointers ;)) on how to fix this issue?

I could post all my draw code, but I even tried an empty project, so I'm pretty sure it's not the rest of the code.

Edit: I tried narrowing down the error even more, and it seems that glRasterPos2f is throwing the acces violation (weirdly enough). It's not between any glBegin and glEnd calls, and there is no OpenGL error.

Edit2: After some advice I tried the following code, I got rid of the access violation, but still no text is displayed

glColor3f(0.5f, 0.5f, 0.5f);
glRasterPos2f(0.0f, 0.0f);
std::string str("Hello World");
char* p = new char[strlen(str.c_str() + 1)];
strcpy(p, str.c_str());
glutBitmapString(GLUT_BITMAP_HELVETICA_12, (const unsigned char*)p);
Roy T.
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  • I'm just guessing, but could it be, that in VC++ 2010 a string literal like "some text" if of type WCHAR*? If so, it would be incompatible to GLUT. That second code looks extremely weird, why that dynamcially allocated char *p? I'd just have used the STL std::string::c_str() function. – datenwolf Mar 28 '11 at 15:59
  • I also tried it with using the c_str() directly, but no effect. It's a really weird problem if you ask me, and probably has something todo with the VC++ 2010 compiler indeed, I'm going to try G++ on a Linux machine today to see if that helps. – Roy T. Mar 29 '11 at 07:29

3 Answers3

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glutBitmapString is of type const unsigned char* and not of unsigned char*. Would that help? I had problems with string casting as well.

And I found out, that I wasn't closing my string, because the unsigned char* should be 1 longer than a string. Here was a snippet that solved it for another method with the same parameter type:

string fullPath = TextureManager::s_sTEXTUREFOLDER + filename;
char *filePath = new char[strlen(fullPath.c_str())+1];
strcpy(filePath,fullPath.c_str());

And then you have your char*.

Marnix
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I recently got the same error while attempting to use glBitmapString(). I was using vs2008. I set a breakpoint at the function call and stepped into it (using freeglut_font.c). Inside I noticed that the exception was being thrown upon what was described to be glut not being initialized. So inside my initialization function I added... 

char* argv[] = {"some","stuff"};    int argc=2;
glutInit(&argc,argv);   
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowPosition(100,100);
glutInitWindowSize(800,600);

Where of course you can use whatever argc/argv you please. This, as well as what was suggested by Marnix solved the exception errors for me.

Note that I don't actually create a window with glut.

viperld002
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-1

Try putting the string in a temporary variable. The fact that you have to cast should raise a red flag.

glColor3f(0.5f, 0.5f, 0.5f);
glRasterPos2f(0, 0);
unsigned char* s = "some text";
glutBitmapString(GLUT_BITMAP_HELVETICA_12, s);

if const doesn't work, then glutBitmapString() may be modifying the string.

Mark
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  • String literals like "some text" are always const signed char*, so I have to cast them to const unsigned char* to use them. (In C your method would probably work). – Roy T. Mar 28 '11 at 14:42