nmappedScratchArea.c

void *newScratchArea(int sizeInBytes) {
     /*
          Create a temporary file. This file will be automatically
          destroyed by the system when our process exits.
     */
     FILE *f = tmpfile();
     if (f) {
          /* Get the file descriptor from the FILE pointer. */
          int fd = fileno(f);
          if (fd >= 0) {
               /* Resize (via ftruncate()) to the size we want. */
               if (0 == ftruncate(fd, sizeInBytes)) {
                    /* Map the file into an unused area of the process's address space. */
                    void *result = mmap(
                         NULL,                    /* No preferred address. */
                         sizeInBytes,             /* Size of mapped space. */
                         PROT_READ | PROT_WRITE,  /* Read/write access. */
                         MAP_FILE | MAP_SHARED,   /* Map from file (default) and map as shared (see above.) */
                         fd,                      /* The file descriptor. */
                         0                        /* Offset from start of file. */
                    );

                    if (result)
                         return result;
               }
          }

          /* failure */
          fclose(f);
     }

     return NULL;
}