Where should be parameters used for output located in the function parameters list

Question

I am trying to decide on a policy regarding the usage of function parameters for output in our C/C++ code.

It is clear to me that the policy should indicate that all parameters used for output should be grouped together either at the end or start of the function parameter list, but I am not sure there are any good reason to prefer either of these locations.

Do you know of any reason to prefer grouping them at the start or at the end?

Answer 1

Just my personal opinion, but if it reflects copy or assignment semantics, then I prefer to put them to the beginning, just like string and certain stdio functions in the C standard library do:

strcpy(dest, src);

looks like

dest = src;

and

fgets(buf, sizeof(buf), file);

looks like

buf = contents_of(file);

If, however, for some reason this is not the case, then I like to organize things so that input comes first, then output, so then I put output arguments at the end of the argument list.