vicky lin <vicky....@gmail.com> writes: > There was something strange happened when I used valgrind. I run > my linux program written in c++ and it threw a "segment fault", but > when I tried " valgrind --tool=memcheck -v ./mycode ", the program > did't throw segment fault and continued to run and returned the > experimental results. [snip] > Are the results got from running under valgrind environment valid?
Well, your program is buggy, but valgrind is doing the best it can under the circumstances. In that sense, the results are "valid". Your code almost definitely has some statement: *x = 42; in it, where `x' points to memory you do not own. In your normal environment, `x' probably points to either memory you don't own, or read-only memory, etc., and thus you get lucky and your program crashes. Under valgrind, that memory is memory that the process owns. This is most likely because valgrind allocates a lot of memory behind your back, and you're happily writing into that "extra" memory. This is basically the same reason that you'll get a segmentation fault on one machine and the program would run to completion on others. The good news is that the "invalid write"s that valgrind reports are almost assuredly the reason for your segfault. That said, if you've got a reproducible case, you're much better off fixing that segfault using gdb before running valgrind. Valgrind tends to be more useful in finding those invalid writes that *don't* cause your program to crash, because those are less visible under normal execution. Cheers, -tom ------------------------------------------------------------------------------ The Planet: dedicated and managed hosting, cloud storage, colocation Stay online with enterprise data centers and the best network in the business Choose flexible plans and management services without long-term contracts Personal 24x7 support from experience hosting pros just a phone call away. http://p.sf.net/sfu/theplanet-com _______________________________________________ Valgrind-users mailing list Valgrind-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/valgrind-users
