Re: assertion "ptr != MAP_FAILED" failed while using mmap

[Ronald Landheer-Cieslak <ronald at landheer dot com>]

On Wed, 25 Jun 2003, Elfyn McBratney wrote:

> On Wed, 25 Jun 2003, Alex Vinokur wrote:
> 
> > ===========================================
> > Windows 2000
> > CYGWIN_NT-5.0 1.3.22(0.78/3/2)
> > GNU gcc version 3.2 20020927 (prerelease)
> > ===========================================
> >
> > Here is some function.
> >
> > --------------------------------------
> > void read_file (char* filename_i)
> > {
> > int fd = open(filename_i, O_RDONLY);
> >   assert (fd > 2);
> >
> > off_t sz = lseek(fd, 0, SEEK_END);
> > char* ptr = (char*)mmap(0, sz, PROT_READ, 0, fd, 0);
> >
> >   assert (ptr != MAP_FAILED);  // Here assertion failed
> >   if (ptr != MAP_FAILED)
> >   {
> >     string str(ptr, ptr+sz);
> >     munmap(ptr, sz);
> >   }
> >
> >   close(fd);
> > }
> > --------------------------------------
> >
> > Assertion  "ptr != MAP_FAILED)" failed.
> > What might cause that?
> 
> This is just a stab in the dark, of course, but surely `ptr != MAP_FAILED'
> would indicate that the mmap did not fail? Assertions (assert()) are based on
> true or false, so the above assert is false in that `ptr != MAP_FAILED'.
> 
> Elfyn
> 
> 
Ehm..

If ptr != MAP_FAILED is not true, that means ptr == MAP_FAILED.
assert(ptr != MAP_FAILED) thus fails if mmap fails..

unless I'm missing something..

rlc



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