Re: Res: [c-prog] Re: integer promotions
It's never a good idea to be running as root... To unsubscribe, send a blank message to mailto:[EMAIL PROTECTED].Yahoo! Groups Links
Re: Res: [c-prog] Re: integer promotions
--- peternilsson42 wrote: -Wconversion Warn for implicit conversions that may alter a value. ... Integral promotions don't alter the value. Maybe you need -Wsign-conversion gcc -Wall -Wsign-conversion problem.c -o problem cc1: error: unrecognized command line option -Wsign-conversion
Re: Res: [c-prog] Re: integer promotions
--- Thomas Hruska wrote:
Try compiling your code as C++ and see if there
is a difference. C++ compilers tend to generate a lot more warnings as
the language is, generally-speaking, more strict.
[EMAIL PROTECTED] ~/programming/c++/problem
$ ls -la
total 10
drwxr-xr-x+ 2 root None 4096 Nov 27 22:47 .
drwxr-xr-x+ 11 root None 4096 Nov 27 22:35 ..
-rw-r--r-- 1 root None 69 Nov 27 22:37 Makefile
-rw-r--r-- 1 root None 261 Nov 27 22:46 problem.cpp
[EMAIL PROTECTED] ~/programming/c++/problem
$ cat problem.cpp
#include climits
#include iostream
using namespace std;
int main (void) {
unsigned short int a;
unsigned long long int b, c;
a = USHRT_MAX;
b = (a*a);
c = ((unsigned int)a*(unsigned int)a);
cout Why hex b != c ?\n;
return 0;
}
[EMAIL PROTECTED] ~/programming/c++/problem
$ cat Makefile
problem : problem.cpp
g++ -Wall -Wconversion problem.cpp -o problem
[EMAIL PROTECTED] ~/programming/c++/problem
$ make
g++ -Wall -Wconversion problem.cpp -o problem
[EMAIL PROTECTED] ~/programming/c++/problem
$ ./problem.exe
Why fffe0001 != fffe0001 ?
Re: Res: [c-prog] Re: integer promotions
On Thu 2008-11-27 16:50:55 UTC-0800, Pedro Izecksohn ([EMAIL PROTECTED]) wrote: [EMAIL PROTECTED] ~/programming/c++/problem $ ls -la total 10 drwxr-xr-x+ 2 root None 4096 Nov 27 22:47 . drwxr-xr-x+ 11 root None 4096 Nov 27 22:35 .. -rw-r--r-- 1 root None 69 Nov 27 22:37 Makefile It's never a good idea to be running as root...
Re: Res: [c-prog] Re: integer promotions
peternilsson42 wrote: Pedro Izecksohn [EMAIL PROTECTED] wrote: peternilsson42 wrote: [ unsigned short int a; a = USHRT_MAX; /* previously a = -1; */] So you made absolutely _no_ change to the semantics of that assignment! I fixed the signal to make others happy. You must be referring to Thomas' comment: BTW, you should have your compiler warnings turned up so that you get a warning for assigning a signed value to an unsigned variable. Admittedly assigning -1 to an unsigned type may look unintuitive, but it's actually the best way to get the max value without using (the ugly) U_MAX macros. So, I disagree with Thomas if he is saying that a = -1; is undesirable. Although I'm all for warnings about comparison of signed and unsigned types. [e.g. -1 1u, which is actually false.] I was actually thinking more along the lines of a forced typecast once the warnings were turned up high enough: a = (unsigned short)-1; There would also have been warnings on the next line of code with the compiler complaining about a signed to unsigned conversion or something like that. That would have been the more useful clue to the OP that a weird conversion was happening behind the scenes. -- Thomas Hruska CubicleSoft President Ph: 517-803-4197 *NEW* MyTaskFocus 1.1 Get on task. Stay on task. http://www.CubicleSoft.com/MyTaskFocus/
Re: Res: [c-prog] Re: integer promotions
--- Thomas Hruska wrote: There would also have been warnings on the next line of code with the compiler complaining about a signed to unsigned conversion or something like that. That would have been the more useful clue to the OP that a weird conversion was happening behind the scenes. Yeah, gcc -Wconversion does not warn about it. Nice comment. May I report this to the gcc maintainers?
Re: Res: [c-prog] Re: integer promotions
Pedro Izecksohn wrote: --- Thomas Hruska wrote: There would also have been warnings on the next line of code with the compiler complaining about a signed to unsigned conversion or something like that. That would have been the more useful clue to the OP that a weird conversion was happening behind the scenes. Yeah, gcc -Wconversion does not warn about it. Nice comment. May I report this to the gcc maintainers? gcc is a very stable compiler and has been around for a really long time. I'm sure there is a way to get the warning level high enough to warn about sign conversions. You could ask them, but try to not present it as a bug - the compiler is the way it is for quite a few historical reasons. One more thing to try: Try compiling your code as C++ and see if there is a difference. C++ compilers tend to generate a lot more warnings as the language is, generally-speaking, more strict. -- Thomas Hruska CubicleSoft President Ph: 517-803-4197 *NEW* MyTaskFocus 1.1 Get on task. Stay on task. http://www.CubicleSoft.com/MyTaskFocus/
