Question

I am working on a C project (still pretty new to C), and I am trying to remove all of the warnings when it’s compiled.

The original coders of this project have made a type called dyn_char (dynamic char arr) and it’s an unsigned char * type. Here’s a copy of one of the warnings:

warning: argument #1 is incompatible with prototype: prototype:
pointer to char : “…/stdio_iso.h”, line 210 argument : pointer to
unsigned char

They also use lots of standard string functions like strlen(); so the way that I have been removing these warnings is like this:

strlen((char *)myDynChar);

I can do this but some of the files have hundreds of these warnings. I could do a Find and Replace to search for strlen( and replace with strlen((char*), but is there a better way?

Is it possible to use a Macro to do something similar? Maybe something like this:

#define strlen(s) strlen((char *)s)

Firstly, would this work? Secondly, if so, is it a bad idea to do this?

Thanks!

Answer 1

This is an annoying problem, but here’s my two cents on it.

First, if you can confidently change the type of dyn_char to just be char *, I would do that. Perhaps if you have a robust test program or something you can try it out and see if it still works?

If not, you have two choices as far as I can see: fix what’s going into strlen(), or have your compiler ignore those warnings (or ignore them yourself)! I’m not one for ignoring warnings unless I have to, but as far as fixing what goes into strlen…

If your underlying type is unsigned char *, then casting what goes into strlen() is basically telling the compiler to assume that the argument, for the purposes of being passed to strlen(), is a char *. If strlen() is the only place this is causing an issue and you can’t safely change the type, then I’d consider a search-and-replace to add in casts to be the preferable option. You could redefine strlen with a #define like you suggested (I just tried it out and it worked for me), but I would strongly recommend not doing this. If anything, I’d search-replace strlen() with USTRLEN() or something (a fake function name), and then use that as your casting macro. Overriding C library functions with your own names transparently is a maintainability nightmare!

Two points on that: first, you’re using a different name. Second, you’re using all-caps, as is the convention for defining such a macro.