ANSI C / assignment makes pointer from integer

[Sebastian Ude]

Assume this (very common) situation:

[...]

char *s;

s = strdup("foo");

[...]

Looks pretty harmless, doesn't it ?
But both gcc 2.95.3 and egcs 1.1.2 give me the following warning when
compiling this code with -ansi:

warning: assignment makes pointer from integer without a cast

The warning disappears if you would change the code like this:

[...]

char *s;

s = (char*) strdup("foo");

[...]

But why ?

What kind of ANSI / ISO rule do I violate ?
Why the hell is a cast neccessary at this point in order not to provoke a
warning when compiling with -ansi ?


Thanks for any explanations,

Sebastian Ude