How to fix warning: attempt to free a non-heap object

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I am compiling a host code using make command. The bellow errors showed up.

The sub code that caused this part of errors:

free(data_point);
    free(host_output);
    free(index_arr);
    free(array_dist);

Errors:

host/src/host.cpp:380:21: warning: attempt to free a non-heap object ‘data_point’ [-Wfree-nonheap-object]
     free(data_point);
                     ^
host/src/host.cpp:381:22: warning: attempt to free a non-heap object ‘host_output’ [-Wfree-nonheap-object]
     free(host_output);
                      ^
host/src/host.cpp:382:20: warning: attempt to free a non-heap object ‘index_arr’ [-Wfree-nonheap-object]
     free(index_arr);
                    ^
host/src/host.cpp:383:21: warning: attempt to free a non-heap object ‘array_dist’ [-Wfree-nonheap-object]
     free(array_dist);

What I have tried:

I tried to comment all the free and the errors are gone. But what I understand is that at the end of the host the memory should be freed up.

Posted 15-Sep-21 3:37am

prother123

Updated 15-Sep-21 4:50am

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OriginalGriff · Answer 1 · 2021-09-15T04:50:00

You should tidy up after yourself, yes - but you can only free object that you have allocated with malloc. You don't free items from the stack, which includes local and global variables, unless they contain a pointer to a heap object (i.e. one created by calling malloc)

That's what the error is telling you - these aren't on the heap, so they can't be freed.
Quite often, that means you've made a major boo-boo, such as returning a pointer to a local variable from a function instead of a heap allocation. I'd start by looking at what they do contain, and where you got it from!