structs created in same address?

This is a discussion on structs created in same address? within the C Programming forums, part of the General Programming Boards category; Hello, I have the following simple program Code: #include <stdio.h> #include <math.h> #define maxG 500 typedef struct _test { float ...

  1. #1
    Registered User nepper271's Avatar
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    structs created in same address?

    Hello,

    I have the following simple program

    Code:
    #include <stdio.h>
    #include <math.h>
    #define maxG 500
    
    typedef struct _test {
        float c[maxG][maxG][maxG];
        int gX, gY, gZ;
    } test;
    
    int main() {
        int i, j, k;
        test p1, p2;
    
        p1.gX = 5;
        p1.gY = 3;
        p1.gZ = 6;
        p2.gX = 2;
        p2.gY = 6;
        p2.gZ = 3;
    
        return 0;
    }
    which compiles, but gives a segmentation fault on execution.

    I'm on Linux, I compiled using gcc or gcc-4.4, and used gdb to debug and obtained the following

    Code:
    Program received signal SIGSEGV, Segmentation fault.
    main () at main.c:17
    17	    p2.gX = 2;
    (gdb) print p1
    Não é possível acessar a memória no endereço 0x7fffffffe228
    (gdb) print &p1
    $1 = (test *) 0x7fffffffe228
    (gdb) print &p2
    $2 = (test *) 0x7fffffffe228
    (gdb) print &p1.c
    $3 = (float (*)[500][500][500]) 0x7fffffffe228
    (gdb) print &p2.c
    $4 = (float (*)[500][500][500]) 0x7fffffffe228
    Now, am I seeing this wrong, or p1 and p2 are occupying the same space? Anyone can give a hint on what I did wrong?

    Thanks a lot,
    Abel

  2. #2
    cas
    cas is offline
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    Your struct contains a 500x500x500 array. On a system with 4-byte floats, that would be 500000000 bytes. That's close a gigabyte (when you take into account the fact that you're trying to create two of those structs), which is almost certainly too large for your stack, which is where your local variables are going.

    You could make the structs global (or static), but that'll still take up a gig of RAM. You probably want to restructure your program.

  3. #3
    Registered User nepper271's Avatar
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    Thank you cas, you are right.

    I have changed maxG to 50 and it worked properly.

    Thanks a lot for the reply,
    Abel

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