How to eliminate warning for passing multidimensional array as const multidimensional array?

Question

Hi,

given the following code:

/* signatures */
int getParams(char params[MAX_PARAM_LEN][MAX_LINE_LEN]);
int getVersion(const char params[MAX_PARAM_LEN][MAX_LINE_LEN],
               const char* tagName );
/* initializing */
char params[MAX_PARAM_LEN][MAX_LINE_LEN] = {};

/* getting parameters */
paramCount = getParams(params); /* OK, params match with getParams signature */

/* processing the params array */
i = getVersion(params, "version"); /* warning: passing arg 1 of `getVersion' from incompatible pointer type */

I see that the constness is the problem, but I don't know why or how to avoid it. What I want is a function which can't modify the params anymore. Any advice is welcome(besides disabling this warning or deleting const in the processing function).

Thanks: Visko

Answer 1

You can't eliminate these warnings in C without making an explicit cast to the proper type. Without a typedef this is going to look ugly though

i = getVersion((const char (*)[MAX_LINE_LEN]) params, "version")

This is a strange quirk specific to C language. In C++ this issue was fixed.

BTW, the {} initializer is illegal in C. How did you manage to get that to compile?

Answer 2

There is no good solution to this problem - I usually just comment out the const qualifier on the function parameter to show that it should ideally be const but that we also want to compile without warnings, i.e.

int getVersion(/* const */ char params[MAX_PARAM_LEN][MAX_LINE_LEN],
               const char* tagName );