C error with structs and pointers

Question

typedef struct stnode {
    unsigned number;
    char * name;
    unsigned section;
    struct stnode * next;
} StudentNode; 

void buildStudentSections(StudentNode * sections[], StudentNode students[], size_t num_students) {

        if(!num_students) return ;
        StudentNode * aux=NULL;

        for(int i=0;i<num_students;i++){

            aux=sections[students[i].section];
            (**(sections+students[i].section)).next=*(students+i);


            }   

    }

When I try do execute this code I have this error:

incompatible types when assigning to type ‘struct stnode *’ from type ‘StudentNode’

What is the problem with the code, I already tried lots of things, but non have worked. I just want to refer the next to the "student" that i'm analyzing

Nim · Accepted Answer · 2013-10-21 13:53:03Z

2

Read the compiler error (you are not executing this code yet - it hasn't compiled...)

‘struct stnode *’ from type ‘StudentNode’

Basically you are trying to assign a structure to a pointer, this doesn't work. Look at the following line:

(**(sections+students[i].section)).next=*(students+i);

The problem lies in the de-reference of (students + 1).

answered Oct 21, 2013 at 13:53

Nim

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4 Comments

user2903358 Over a year ago

Now im receiving the error line 7: 1961 Segmentation fault Why?

Nim Over a year ago

We cannot answer this, you need to debug - get the program to generate a core file and then fire up your debugger and look at the core.

ryyker Over a year ago

Without seeing how this is called, there is no way to know exactly how the fault is occurring.

user2903358 Over a year ago

int main() { StudentNode student = { 11111, "Afonso Henriques", 1, NULL }; StudentNode * sections[3] = { NULL, NULL, NULL }; buildStudentSections(sections, &student, 1); return 0; }

Marius Bancila · Accepted Answer · 2013-10-21 13:54:19Z

1

The problem is that *(students+i) is de-referencing the element students+i. It should be:

(**(sections+students[i].section)).next=students+i;

answered Oct 21, 2013 at 13:54

Marius Bancila

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1 Comment

user2903358 Over a year ago

Now im receiving the error line 7: 1961 Segmentation fault Why?

ryyker · Accepted Answer · 2013-10-21 14:26:51Z

Change this:

void buildStudentSections(StudentNode * sections[], StudentNode students[], size_t num_students) {

        if(!num_students) return ;
        StudentNode * aux=NULL;

        for(int i=0;i<num_students;i++){

            aux=sections[students[i].section];       // = *(x) you are dereferencing students+1
            (**(sections+students[i].section)).next=*(students+i);


            }   

    }

To this:

void buildStudentSections(StudentNode * sections[], StudentNode students[], size_t num_students) 
{

        if(!num_students) return ;
        StudentNode * aux=NULL;

        for(int i=0;i<num_students;i++)
        {

            aux=sections[students[i].section];      //removed '*`
            (**(sections+students[i].section)).next = (students+1); 


        }   

}

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