Replacement for NSAddImage (in GLLoadGen) - c

Question

The GL loader generated with GLLoadGen contains the following code:
static void* AppleGLGetProcAddress (const GLubyte *name)
{
static const struct mach_header* image = NULL;
NSSymbol symbol;
char* symbolName;
if (NULL == image)
{
image = NSAddImage("/System/Library/Frameworks/OpenGL.framework/Versions/Current/OpenGL", NSADDIMAGE_OPTION_RETURN_ON_ERROR);
}
/* prepend a '_' for the Unix C symbol mangling convention */
symbolName = (char*)malloc(strlen((const char*)name) + 2);
strcpy(symbolName+1, (const char*)name);
symbolName[0] = '_';
symbol = NULL;
/* if (NSIsSymbolNameDefined(symbolName))
symbol = NSLookupAndBindSymbol(symbolName); */
symbol = image ? NSLookupSymbolInImage(image, symbolName, NSLOOKUPSYMBOLINIMAGE_OPTION_BIND | NSLOOKUPSYMBOLINIMAGE_OPTION_RETURN_ON_ERROR) : NULL;
free(symbolName);
return symbol ? NSAddressOfSymbol(symbol) : NULL;
}
This function apparently loads the address of the OpenGL function name. However the calls to NSAddImage and related are deprecated since OSX 10.5. What is the current (non-deprecated) approach to load the function addresses?

Answer 1

dlopen(), dlsym() and friends are probably the best option. This will also make your code more portable, since they are available on most Unix systems as well.
Following is some code I've used in the past to load GL functions on Mac OSX (tested on version 10.8, should still work OK for Mavericks):
// Handle to the OpenGL dynlib:
static void * glLibrary;
// Path to GL on OSX. True for version 10.8.
static const char * glLibPath = "/System/Library/Frameworks/OpenGL.framework/Versions/Current/OpenGL";
// Loads the OpenGL library:
void LoadGL()
{
// Load GL dynlib:
glLibrary = dlopen(glLibPath, RTLD_LAZY);
if (!glLibrary)
{
const char * error = dlerror();
// handle error
}
}
// Unloads the GL library:
void UnloadGL()
{
if (glLibrary)
{
if (dlclose(glLibrary) != 0)
{
// problem...
}
glLibrary = NULL;
}
}
// Grab a function pointer form the previously loaded GL library:
void * GetGLFunctionPointer(const char * funcName)
{
assert(funcName != NULL);
assert(glLibrary != NULL && "OpenGL dynlib not yet loaded!");
return dlsym(glLibrary, funcName);
}
// Usage example:
int main()
{
LoadGL();
void * fn = GetGLFunctionPointer("glEnable");
assert(fn != NULL);
UnloadGL();
return 0;
}