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c++arraysstructmemcpymemmove

memcpy issue -> trying to copy an array of struct

I am completely lost on why memcpy or memmove is not working for me.

I am trying to copy a array of struct (joblist) to another array of same struct (Q) to use for data manipulation, while keeping my original array intact.

I have spent a lot of time on SO and google troubleshooting this and I cannot find out why it won't work.

    Q = new AdjacencyList[numjobs + 1]; //create a queue
    // Q = joblist;
    memmove(&Q, &joblist, sizeof(AdjacencyList) );
    Q[0].jobnum = 30;

I tried to just make Q = joblist, but then when I changed a value in one, it changed in both.

    struct AdjacencyList  {
    NodeType state; // what is present state of job? 
    NodePath path; // is job part of critical path?
    int jobnum;
    int edges;     
    int tocount;
    int fromcount;          
    int to[50];      
    int from[50]; 
    };
    AdjacencyList *joblist;
    AdjacencyList *Q;

This is the struct I created.

*** Error in `p5.out': corrupted double-linked list: 0x0989e8c0 ***
======= Backtrace: =========
/lib/libc.so.6[0x47975143]
/lib/libc.so.6[0x4797b984]
/lib/libc.so.6[0x4797cd28]
/lib/libstdc++.so.6(_ZdlPv+0x20)[0x47d8d9e0]
/lib/libstdc++.so.6(_ZdaPv+0x1c)[0x47d8da3c]

Any help would be greatly appreciated. Thanks.

SUB

Solution

  • They way you call memmove(dst, src, sizes). Is not correct. It should be 

    memmove(Q, joblist, sizeof(AdjacencyList) * (numjobs + 1));

    UPDATE:

    Like its name, memmove operates on memory. It simply copies sizes bytes data from src to dst.

    If you want to copy an array of n objects to Q, you must tell the function the total size of the data you want to copy, that is size of each objects * number of objects. I don't know how many objects you need to copy, numjobs + 1 is only an example. If you want to copy numjobs it should be sizeof(AdjacencyList) * numjobs.