This function returns the value of the system global variable currentA5. The currentA5 value is a pointer to a location within the memory space allotted for your program; every currently running program has its own individual currentA5 value. currentA5 points to the first byte of your program's application parameters. The memory space immediately preceding the location pointed to by currentA5 contains your program's global variables. See the "Introduction to Memory Management" chapter in Inside Macintosh: Memory for more information. This function is available only for 68K compilation.
Inside Macintosh: Memory