On Apr 11 20:25, Christoph Weise wrote: > Please see below, I provide minimal C code for three separate > executables, one creates the shm section, another finds it, the third > removes it. I include also a bash test script that executes the > routines in order.
Thanks, > Please beware as I removed some checks to reduce > the length of the code, but it should run ok. The PAGESIZE parameter > is hardcoded (here 512 bytes). The desired shared mem section size is > set interactively as input to makeshm, or automatically with the bash > script. Ok, but there are bugs in the code which result in GCC warnings. I don't know which of them are part of your original code, but they are really a problem. if ((int) -1 == p) Don't check a pointer against an int value. It won't work on a 64 bit platform. Make that if ((void *) -1 == p) For the same reason, don't use %x to printf a pointer. Use %tx. > I can write to the shm section with the second routine when the requested > section <= 4096 bytes. Otherwise it's not happy. The problem is the call to shmget: #undef PAGESIZE #define PAGESIZE 512 shmid = shmget(key, PAGESIZE, IPC_ALLOC); Since you're requesting only 512 bytes, the shared memory segment the following shmat call returns is only 4K. The shmget call should request as much memory as it needs so that the OS call is called with the right view size. I re-read the POSIX man page for shmget, and it doesn't mention anything which would point out that Cygwin's behaviour here is wrong. If anybody has more information on this, please share them. HTH, Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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