What does g CTRL-A really do?

Question

Today I had that old feeling of wonder on how powerful VIM is: I needed a number sequence in the start of some fields and discovered the power of g CTRL-A.

So as I always do when I discover something new in VIM I tried to find exactly what this command does, but was baffled to see what :h g told me about g CTRL-A:

g_CTRL-A    g CTRL-A       only when compiled with MEM_PROFILE
                           defined: dump a memory profile

Huh? What's a "memory profile"? what does that have to do with number sequences? I try to use g CTRL-A in other element besides a blockwise selection of numbers and it did nothing.

Can anyone explain what exactly g CTRL-A does and what a memory profile is?

Edit

As @MDeBusk correctly pointed out, that wasn't the correct help entry. A bit down below we see the correct entry as the following:

v_g_CTRL-A  g CTRL-A    2  add N to number in highlighted text

That's better. The former entry was for normal mode. But when using in a selection we're on visual mode.

Fine. But the question remains: what does g CTRL-A on normal mode do? What's a memory profile? Does anyone know?

Answer 1

But the question remains: what does g CTRL-A on normal mode does ? What's a memory profile ? Anyone knows ?

This refers to this bit of code from src/feature.h:

/*
 * MEM_PROFILE      Debugging of memory allocation and freeing.
 */
// #define MEM_PROFILE

If you remove the // comment symbol at the start of that line (or just add -DMEM_PROFILE to your compiler command line), this will define a C preprocessor variable called MEM_PROFILE. That will in turn enable other code in other files that tracks calls to allocate and free memory and a function called vim_mem_profile_dump(). When that function is compiled into Vim it's called when you use the normal mode g CTRL-A command and when Vim exits.

That function just prints some information about the memory allocations and deallocations that Vim has done to that point:

    printf(_("\n[bytes] total alloc-freed %lu-%lu, in use %lu, peak use %lu\n"),
        mem_allocated, mem_freed, mem_allocated - mem_freed, mem_peak);
    printf(_("[calls] total re/malloc()'s %lu, total free()'s %lu\n\n"),
        num_alloc, num_freed);

This is debugging information that might be of interest to a developer working on the Vim source code. For regular users it won't be of much, if any, interest, which is why it's disabled by default.

Answer 2

You're looking at the help for g_CTRL-A in normal mode, but when you're incrementing a list of numbers, you're in visual mode.

I'm sorry; I don't know what a memory profile is exactly. It's related to debugging and requires vim to be compiled with that purpose in mind. When I type g_CTRL-A in normal mode, I don't notice anything happening. I didn't compile it with MEM_PROFILE, so I imagine nothing does happen.