Unhandled Exception, Access Violation

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the program run perfect when the program use the data from the coding.
but when i try to import from txt file he make a problems.
the code of the import from txt is working

i got message error
Unhandled exception at 0x014621fa in Tanks.exe: 0xC0000005: Access violation reading location 0xfeeefeee.

and it point to line

C++

void Graph::addEdge(int u, int v) {
    A[u-1][v-1] =1; 
THIS LINE->	A[v-1][u-1] = 1;
}

the fun get 1 and 2.
really dont know why the problem

reply to Sergey-
yeah ofcourse its just comment that i added here.

did few times debug and same error.
if i put data in my code like
g.addEdge(1, 2); g.addEdge(1, 3);
g.addEdge(2, 3); g.addEdge(2, 4);
g.addEdge(3, 4); g.addEdge(4 ,5);

it works perfect. but when i add g.addedge between the lines of import from txt and show the problem.

Posted 8-Jan-16 6:55am

Ben ----

Updated 8-Jan-16 7:16am

v2

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Comments

Sergey Alexandrovich Kryukov 8-Jan-16 13:10pm

You simply address beyond the memory fragment allocated for A. You did not show what it is. Just check up everything thoroughly, use the debugger.

"THIS LINE" should be your comment in your code sample, not the "code" which won't compile.

—SA

Foothill 8-Jan-16 15:49pm

If you always perform a boundry check on any index accessor before you use it, you can preven this problem and many others as well. IIRC, the Heartbleed bug was caused by a function that didn't validate a parameter before using it to access an array.

Jochen Arndt 8-Jan-16 15:51pm

Sergey already told you what is happening:
You are accessing A out of bounds.

Probable error sources are calling addEdge with u greater than the x size of the array, and/or v greater than the y size of the array (array allocated as A[x][y]), or with u and/or v less or equal to zero.

Sergey Alexandrovich Kryukov 8-Jan-16 16:58pm

Also, A could be anything, including null or some non-initialized garbage.
—SA

[no name] 8-Jan-16 22:03pm

Are you using visual studio. Which version? However only one way to solve it (we can't do it for you) - learn to use assert() and your debugger.

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KarstenK · Answer 1 · 2016-01-08T23:16:00

Solution 1

write some check code in your function like:

C++

void Graph::addEdge(int u, int v) {
  ASSERT( (u>0) && (v>0) ); //!!!! 0 is valid (my tip)
  ASSERT( (u    A[u-1][v-1] =1; 
}

writing some error check and test code is good style and always paying off. ;-)

Posted 8-Jan-16 23:16pm

KarstenK