Memory mapping in Objective-C

gistfile1.txt

const char* cstr = [string UTF8String];

void* anon = mmap(0, sizeof(char) * (string.length + 1), PROT_WRITE|PROT_READ, MAP_ANON|MAP_PRIVATE, 0, 0);
if (anon == MAP_FAILED) {
  NSLog(@"Failed to map memory.");
  return;
}
strcpy(anon, cstr);

// How do I get a file descriptor for use here?
markdownin = fdopen(fd, "r");

As this stands I'm able to map the memory, but I don't have a file descriptor that I can use between mmap and f*open methods so that I can create a FILE pointer.

1. Use shm_open to obtain file descriptor.
2. Use file descriptor from shm_open in mmap.
3. Use fdopen to obtain FILE pointer from file descriptor.

This looks perfect. Will test it out when I get home. Thanks! On Jun 24, 2012, at 6:19 PM, Vladimir Grichina < [email protected]> wrote: 1. Use `shm_open` to obtain file descriptor. 2. Use file descriptor from `shm_open` in `mmap`. 3. Use `fdopen` to obtain `FILE` pointer from file descriptor.

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Here's the latest. Still not working sadly and I'm not sure what the culprit is.

const char* path = "/string1524";
int stringSize = sizeof(char) * (string.length + 1);
int fd = shm_open(path, O_RDWR | O_CREAT);
ftruncate(fd, stringSize);
void* anon = mmap(0, stringSize, PROT_WRITE|PROT_READ, MAP_SHARED, fd, 0);
if (anon == MAP_FAILED) {
  NSLog(@"Failed to map memory.");
}
strcpy(anon, cstr);

// This returns a FILE*, but when trying to read from it I get garbage data.
markdownin = fdopen(fd, "r");

Unfortunately I also in result had no success in making it work on OS X / iOS.

However I found alternative solution which even isn't an ugly hack – http://developer.apple.com/library/ios/#documentation/System/Conceptual/ManPages_iPhoneOS/man3/fropen.3.html
You can just specify your function to read stream.

There is example here https://redmine.openinfosecfoundation.org/attachments/105/0001-fmemopen-wrapper-added-fix-compilation-problems-on-m.patch

I used this code linked to by poTomek on twitter and it worked beautifully:

https://github.com/ingenuitas/python-tesseract/blob/master/fmemopen.c

Looks very similar to the example given in your links :)

http://jverkoey.github.com/fmemopen/

Thanks gang!