Segementation Problem while accessing contents from Memory Mapped File

[nkrisraj]

Hi,

I have a following structure:
typedef struct
{
RateData rdr;
int RateID;
char RateBalance;
} RateInfo;


typedef struct
{
DayRates *dr;
WeekRates *wr;
} TimeOfDayRates;

First I will create the memoefy for the DayRates, WeekRates structures
inside the RateInfo structure variable. After that Iam going to copy
the contents into DayRates, WeekRatesstructures. Once the all the
structure members inside RateInfo structure variable are initialized, I
will add that node to a AVL tree. This way, Iam going to create an AVL
tree by adding RateInfo nodes to it. Once the total tree is contructed,
I will store this tree as file (rateinfo.map) on the disk.

In my next programming component, Iam going to load this file
(rateinfo.map) into memory using mmap() function call. Once I load the
file into memory using mmap(), Iam able to access the RateID and
RateBalance members of the RateInfo. But, Iam not able to access the
DayRates, and WeekRates structure contents. When I try to access the
members of DayRates , and WeekRates structures, my program is showing
segmentation fault and Iam getting the core dump.

Even though I allocated memory for DayRates , and WeekRates structures
inside RateInfo node while creating the tree, why Iam not able to
access contents of DayRates , and WeekRates structures when I mmap()
file into memory?

Any pointers would be a great help.

Thanks,
-Nikhil

 

[nkrisraj]

Please find the correct structure declarations:
typedef struct
{
RateData rdr;
int RateID;
char RateBalance;

} RateInfo;

typedef struct
{
DayRates *dr;
WeekRates *wr;

} RateData;

 

[Keith Thompson]

In my next programming component, Iam going to load this file
(rateinfo.map) into memory using mmap() function call. Once I load the
file into memory using mmap(), Iam able to access the RateID and
RateBalance members of the RateInfo. But, Iam not able to access the
DayRates, and WeekRates structure contents. When I try to access the
members of DayRates , and WeekRates structures, my program is showing
segmentation fault and Iam getting the core dump.

Even though I allocated memory for DayRates , and WeekRates structures
inside RateInfo node while creating the tree, why Iam not able to
access contents of DayRates , and WeekRates structures when I mmap()
file into memory?

There is no mmap() function in standard C (it's defined by POSIX, a
separate standard). You'll need to ask in a newsgroup for your
system, perhaps comp.unix.programmer.

 

[Walter Roberson]

There is no mmap() function in standard C (it's defined by POSIX, a
separate standard).

True, but his real problem was in trying to use a pointer created
in one execution in a different execution. He could have just
read() the same data into a block of memory and tried to use it,
to the same failed effect. mmap() was a red herring in this problem.