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Invalid read of size 1

Posted on 2008-10-15
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i am getting error : invalid read of size 1...

what does this mean...
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Question by:zizi21
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sunnycoder earned 1200 total points
ID: 22723484
You are reading one byte from memory that you have not allocated
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Author Comment

by:zizi21
ID: 22723505
is there a way to check which memory i have not allocated ? i am using valgrind
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by:zizi21
ID: 22723509
with this options:valgrind --tool=memcheck --leak-check=yes --show-reachable=yes
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by:Infinity08
Infinity08 earned 800 total points
ID: 22723520
You should have a backtrace that goes with the error. That shows you the exact location of the problem.
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Expert Comment

by:sunnycoder
ID: 22723527
It should be giving you a stack trace
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by:zizi21
ID: 22723537
it says at 0x804A936:funct1(....)

it does not say the exact location..is there any option that i should use...
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by:sunnycoder
ID: 22723563
There should be more .. something like

==9814==  Invalid write of size 1
==9814==    at 0x804841E: main (example2.c:6)
==9814==  Address 0x1BA3607A is 0 bytes after a block of size 10 alloc'd
==9814==    at 0x1B900DD0: malloc (vg_replace_malloc.c:131)
==9814==    by 0x804840F: main (example2.c:5)

The values in the bracket are file name and line number
Can you copy paste the exact output.
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Author Comment

by:zizi21
ID: 22723568
=11411== Invalid read of size 1
==11411==    at 0x804A936: computeA (in /test/main)
==11411==    by 0x804B0E1: scan(in /test/main)
==11411==    by 0x8048EFF: main (main.c:262)
==11411==  Address 0x1EC1C029 is 0 bytes after a block of size 52428801 alloc'd
==11411==    at 0x1B904984: malloc (vg_replace_malloc.c:131)
==11411==    by 0x8048AC3: main (main.c:162)
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Author Comment

by:zizi21
ID: 22723582
i went to the computeA function but i can't say which line it is happening...
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by:sunnycoder
ID: 22723707
This is odd ... it would print line numbers for only part of the trace. As far as I can tell your command line looks okay. Did you really allocate 52428801 bytes of memory? Wondering if the tool got clobbered ;-) Or were there some memory errors preceding this one?
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by:zizi21
ID: 22723810
it is the first error and i have more similar errors after this...

i checked and i did allocate memory for 52428801
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by:Infinity08
ID: 22723880
>> i went to the computeA function but i can't say which line it is happening...

Can you show the computeA function ?
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Author Comment

by:zizi21
ID: 22724047
actually, the code is very very long and i am not allowed to post any code as i would be penalised...i am a student...

i am grateful of all of you helping ...sorry for that...
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Expert Comment

by:Infinity08
ID: 22724335
>> the code is very very long

It is a good idea to split up your code into manageable functions (no longer than 10-15 lines is a good rule). Longer functions are more difficult to maintain, and it's easier to make mistakes.


You can look for the problem yourself, by checking all the locations where memory is read, and checking whether the reads are done within allocated memory blocks.
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by:sunnycoder
ID: 22728025
You can probably zip the code and upload to another site such as rapidshare or even ee-stuff.com and post a link here. Once we have found the problem, you can delete the file from the server.
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Author Comment

by:zizi21
ID: 22765199
just saw this...the thing is solved ..thanks a million
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