#include <stdio.h>
char str[] = "abc";
const char *a1 = str;
struct A { operator const char *() {return str;} } a2;
volatile char *b1 = str;
struct B { operator volatile char *() {return str;} } b2;
int
main()
{
printf ("%p\n", a1);
printf ("%p\n", b1);
printf ("%p\n", (const char *)a2);
printf ("%p\n", (volatile char *)b2);
printf ("%d\n", a1 - b1);
printf ("%d\n", (const char *)a2 - (volatile char *)b2);
printf ("%d\n", a2 - b2); // error reported here
return 0;
}
gives:
t.cpp: In function int main():
t.cpp:22: error: no match for operator- in a2 - b2
t.cpp:22: note: candidates are: operator-(volatile char*, volatile char*)
<built-in>
t.cpp:22: note: operator-(const char*, const char*) <built-in>
However, lines 20 and 21 clearly do the same operation, but slightly
differently. These lines appear to be able to convert the types, presumably
according to clause 4.4 of the C++ standard, but the last example cannot. Yet
the error message shows that it has found the right conversion operators.
EDG 3.0 compiles this without any issues.
Note: the correct behaviour of this program is to print the same pointer four
times, and then print zero three times.
--
Summary: can't subtract 'volatile char *' from 'const char *'
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: andrew dot stubbs at st dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29148
