Paolo Carlini <[EMAIL PROTECTED]> writes: | Hi Manuel, | | >> in a nutshell, what is happening is that a difference of two pointers is | >> assigned to an unsigned variable. First blush, the warning seems to me a | >> bit overzealous, but if we concur that this is what we *really* want for | >> 4.3, we can change the affected (very old, indeed) lines of code, no | >> problem at all. | > | > Hi Paolo, | > | > Wconversion is supposed to warn for conversions that may change a | > value. Can the resulting value change when converted to unsigned? If | > so, the warning is warranted (I think). | > | > Anyhow, Wconversion needs fine-tuning and I prefer for it to be useful | > rather than to literally follow its definition, so if this operation | > is quite frequent and safe, I could detect it and avoid the warning. | > | > I am no GCC or C++ expert, so please give me more information on the | > issue and feedback from others would be appreciated. | | Well, just have a look to Gerald' examples: it's old HP / SGI STL | code, we are assigning / initializing a size_t from a pointer | difference, or arithmetic, more generally. There are quite a few | instances of the issue, beyond that pointed out by Gerald. Certainly, | the HP / SGI engineers considered those assignment harmless, and I | respect that kind of assessment, but on the other hand, at the time | the compilers were probably weaker at warning, I'm not sure. All in | all, I think we can definitely add casts to the library, would be only | a few tens of lines worth of patch, I think. Whether the warning is | useful to the entire GCC community, I cannot say... But I hope we can | resolve the issue rather quickly, because, in case, I'd like to start | the audit of the library as soon as possible and be done with the | issue as far as we are concerned...
There is something that we knoq about the code, that the compiler does not have: we expect a sequence denoted by its first and last element, so that the difference is always positive. However, the difference of pointers is defined in the language as an ptrdiff_t (a signed type). No wonder what people invented ssize_t :-) I believe we have to investigate further what promises we want make and hold through max_size() and change the code according to that. -- Gaby
