>From INT.h.in:
828 #if !defined(@KWIML@_INT_NO_INTPTR_T)
829 @KWIML@_INT__VERIFY_TYPE(@KWIML@_INT_intptr_t, sizeof(void*));
830 #endif
831 #if !defined(@KWIML@_INT_NO_UINTPTR_T)
832 @KWIML@_INT__VERIFY_TYPE(@KWIML@_INT_uintptr_t, sizeof(void*));
833 #endif
Now this statement blows up in the make Makefile process as follows:
cmIML_INT__VERIFY_TYPE(cmIML_INT_intptr_t, sizeof(void*));
^
%CXX-E-NOTCOMPREDEC, declaration is incompatible with
"int (*cmIML_INT_intptr_t__VERIFY__)[4U]" (declared at line 829)
at line number 829 in file LCL_ROOT:[cmake-3_3_2.Bootstrap_cmk.cmIML]INT.h;11
I wrote a simple C application to confirm the compiler's values,
compiled-and-linked the application on both OpenVMS and Fedora Linux (x64) and
noticed a discrepancy...
ITAN1* ty foo.c
#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
int main(void) {
printf( "sizeof(intptr_t) = %d\n", sizeof(intptr_t));
printf( "sizeof(uintptr_t) = %d\n", sizeof(uintptr_t));
printf( "sizeof(void *) = %d\n", sizeof(void *));
return EXIT_SUCCESS;
}
On OpenVMS this application displays the following:
ITAN1* r foo
sizeof(intptr_t) = 8
sizeof(uintptr_t) = 8
sizeof(void *) = 4
sizeof(int *) = 4
and clearly sizeof(void *) = 4 < does NOT equal > sizeof(intptr_t) = 8
On Fedora22 the exact same application displays the following:
[jpcustin@localhost ~]$ ./foo
sizeof(intptr_t) = 8
sizeof(uintptr_t) = 8
sizeof(void *) = 8
sizeof(int *) = 8
[jpcustin@localhost ~]$
http://en.cppreference.com/w/c/types/integer describes intptr_t as: "integer
type capable of holding a pointer"
http://pubs.opengroup.org/onlinepubs/009695399/basedefs/stdint.h.html goes a
little further:
Integer types capable of holding object pointers
The following type designates a signed integer type with the property that any
valid pointer to void can be converted to this type, then converted back to a
pointer to void, and the result will compare equal to the original pointer:
intptr_t
The following type designates an unsigned integer type with the property that
any valid pointer to void can be converted to this type, then converted back to
a pointer to void, and the result will compare equal to the original pointer:
uintptr_t
This begs the question...
Why does the CMake test rely on checking if sizeof(intptr_t) equals sizeof(void
*)
instead of sizeof(intptr_t) greater than or equal to sizeof(void *)
(so can an intptr_t "hold" a void *)?
JayC
--
Powered by www.kitware.com
Please keep messages on-topic and check the CMake FAQ at:
http://www.cmake.org/Wiki/CMake_FAQ
Kitware offers various services to support the CMake community. For more
information on each offering, please visit:
CMake Support: http://cmake.org/cmake/help/support.html
CMake Consulting: http://cmake.org/cmake/help/consulting.html
CMake Training Courses: http://cmake.org/cmake/help/training.html
Visit other Kitware open-source projects at
http://www.kitware.com/opensource/opensource.html
Follow this link to subscribe/unsubscribe:
http://public.kitware.com/mailman/listinfo/cmake
