On Aug 20, 2007, at 2:07 PM, mabshoff wrote:
>> However, there is one "error" which valgrind reports on my own code >> from time to time which I have been unable to determine the source >> of. >> It says something like "conditional jump depends on uninitialised >> data". I have stared at code for hours trying to determine where >> these >> errors come from. I still have code for which I have been unable to >> eliminate such errors. >> > > That usually happens in the following circumstance: > > int i; // this is initialized to zero on any sane system, i.e. > anywhere but Windows :) To make sure I know what's going on, this for "static" variables, i.e., those declared outside the scope of a procedure, or explicitly static within a procedure. > if (i>0) > do something; If the above sequence is literally what's in the file, then it is an uninitialized variable, right? > Now valgrind assumes that "conditional jump depends on uninitialised > data", i.e. "i". Well, but it is zero anyway would one say. And you > would be correct in 99% of all cases, but I fixed a bug very similar > to the above in LinBox about 4 weeks ago that caused a crash on Debian > unstable's gcc but not with the other 10 compilers I tried. Lesson > lerned. The assigment to zero puts i into another segment, so many > people avoid it. I don't understand your last comment: are you saying that using "int i = 0;" is something that most people avoid? Why? (I understand the 'segment' part; this puts 'i' in a segment of initialized data; otherwise, it's up to the runtime to initialize a chunk of memory with zeros and 'i' is in that segment (which is not in the file, only created at runtime)). A compiler that does anything else isn't a 'C' compiler :-} Justin -- Justin C. Walker, Curmudgeon at Large Institute for the Absorption of Federal Funds ----------- My wife 'n kids 'n dogs are gone, I can't get Jesus on the phone, But Ol' Milwaukee's Best is my best friend. ----------- --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
