Question

Note: when I say “static string” here I mean memory that can not be handled by realloc.

Hi, I have written a procedure that takes a char * argument and I would like to create a duplicate IF the memory is not relocatable/resizable via realloc. As is, the procedure is a ‘heavy’ string processor, so being ignorant and duplicating the string whether or not it is static will surely cause some memory overhead/processing issues in the future.

I have tried to use exception handlers to modify a static string, the application just exits without any notice. I step back, look at C and say: “I’m not impressed.” That would be an exception if I have ever heard of one.

I tried to use exception handlers to call realloc on a static variable… Glib reports that it can’t find some private information to a structure (I’m sure) I don’t know about and obviously calls abort on the program which means its not an exception that can be caught with longjmp/setjmp OR C++ try, catch finally.

I’m pretty sure there must be a way to do this reasonably. For instance dynamic memory most likely is not located anywhere near the static memory so if there is a way to divulge this information from the address… we might just have a bingo..

I’m not sure if there are any macros in the C/C++ Preprocessors that can identify the source and type of a macro argument, but it would be pretty dumb if it didn’t. Macro Assemblers are pretty smart about things like that. Judging by the lack of robust error handling, I would not be a bit surprised if it did not.

Answer 1

You may be able to detect ranges of memory and do some pointer comparisons. I’ve done this in some garbage collection code, where I need to know whether a pointer is in the stack, heap, or elsewhere.

If you control all allocation, you can simply keep min and max bounds based on every dynamic pointer that ever came out of malloc, calloc or realloc. A pointer lower than min or greater than max is probably not in the heap, and this min and max delimited region is unlikely to intersect with any static area, ever. If you know that a pointer is either static or it came from malloc, and that pointer is outside of the “bounding box” of malloced storage, then it must be static.

There are some “museum” machines where that sort of stuff doesn’t work and the C standard doesn’t give a meaning to comparisons of pointers to different objects using the relational operators, other than exact equality or inequality.