qsort on multiple indexes ex. primary index then secondary index

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  1. #1
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    Exclamation qsort on multiple indexes ex. primary index then secondary index

    What would be the best way to implement a qsort that does sort on multiple indexes. ex. first sort on primary index then secondary index.

    Code:
    //before sort: {(0, 3),(1, 2),(0, 1)}
    //after sort: {(0, 1),(0, 3),(1, 2)}

    Code:
    typedef struct{
    boolean element1;//primary
    int element2;//secondary
    }foo
    
    int my_cmp(){
    //?? what would be the most efficient implementation
    }
    int main(){
    foo a[20]; 
    //assume the array gets filled here
    
    qsort(&a[0], sizeof(a),sizeof(a[0]), my_cmp);
    
    return 0;
    }
    Thank you!

  2. #2
    and the hat of wrongness Salem's Avatar
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    It basically goes like this
    Code:
    if ( a.e1 < b.e1 ) return -1;
    if ( a.e1 > b.e1 ) return +1;
    // e1 is equal, now go onto e2
    if ( a.e2 < b.e2 ) return -1;
    if ( a.e2 > b.e2 ) return +1;
    // all the keys are equal
    return 0;
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