problem with structure

**zetaXX** · 05-27-2013

Hey! I just started with structs so it probably will be a stupid fail, but I dont give with the clue! Thats part of my code:

Code:

struct Array{
       int v[];
       int n;
};


Array ArrayCreaAleatorio(int linf,int lsup){


int linf2;
linf2 = linf; 
      struct Array array1;
      array1.n = lsup-linf+1;
      for (int i = 0; i=n; i++){
      array1.v[i] = linf2++;
      linf2 = linf2++;
      }


 for (int j = 0; j = (n-2); j++){
     v.array1[j] = (rand()% lsup)+linf;
     }  
return array1;  
}

And I get these errors:
`n' undeclared (first use this function)
`v' undeclared (first use this function)

**ZuK** · 05-27-2013

`n' undeclared (first use this function) -> should be array1.n
`v' undeclared (first use this function) -> should be array1.v

You have to allocate some memory for array1.v, as is array1.v points to a random location

Kurt

**rcgldr** · 05-27-2013

Assuming your compiler supports variable size arrays at the end of a struct, you need to change the order of the struct to:

Code:

struct Array{
    int n;
    int v[];
};

You will also have to allocate memory (malloc()) for this structure, since the size of the struct is variable.

**zetaXX** · 05-27-2013

Originally Posted by ZuK

`n' undeclared (first use this function) -> should be array1.n
`v' undeclared (first use this function) -> should be array1.v

You have to allocate some memory for array1.v, as is array1.v points to a random location

Kurt

And how do I do it?

**rcgldr** · 05-27-2013

Originally Posted by zetaXX

And how do I do it?

example program that uses typedefs:

Code:

#include <malloc.h>

typedef struct Array{
    int n;
    int v[];
}Array_t, *PArray_t;

int main(int argc, char *argv[])
{
int i;
int size = 10;
PArray_t pArray;

    pArray = malloc(sizeof(Array_t) + size*sizeof(int));

    pArray->n = size;
    for(i = 0; i < size; i++)
        pArray->v[i] = i;

    free(pArray);

    return(0);
}

For a more generic allocation based on the size of an element of v you could use:

Code:

    pArray = malloc(sizeof(Array_t) + size*sizeof(((PArray_t)0)->v[0]));

**zetaXX** · 05-27-2013

Originally Posted by rcgldr

example program that uses typedefs:

Code:

#include <malloc.h>

typedef struct Array{
    int n;
    int v[];
}Array_t, *PArray_t;

int main(int argc, char *argv[])
{
int i;
int size = 10;
PArray_t pArray;

    pArray = malloc(sizeof(Array_t) + size*sizeof(int));

    pArray->n = size;
    for(i = 0; i < size; i++)
        pArray->v[i] = i;

    free(pArray);

    return(0);
}

For a more generic allocation based on the size of an element of v you could use:

Code:

    pArray = malloc(sizeof(Array_t) + size*sizeof(((PArray_t)0)->v[0]));

So I have to use malloc on my struct?
I mean

v = (int*)malloc ( n*sizeof(int) );It is right?

**rcgldr** · 05-27-2013

Originally Posted by zetaXX

So I have to use malloc on my struct?

v = (int*)malloc ( n*sizeof(int) );It is right?

You need to use malloc for the entire struct if you use the example I posted before.

If you only want to allocate v, then your struct needs to be changed to:

Code:

struct Array{
    int n;
    int *v;
};

**zetaXX** · 05-27-2013

Originally Posted by rcgldr

You need to use malloc for the entire struct if you use the example I posted before.

If you only want to allocate v, then your struct needs to be changed to:

Code:

struct Array{
    int n;
    int *v;
};

but I need to V to be an array not a pointer lol!
I cant uderstand you I think xD

**rcgldr** · 05-27-2013

Originally Posted by zetaXX

int *v; ... but I need to V to be an array not a pointer.

You can use it as an array, even though it's a pointer, for example, v[i].

**zetaXX** · 05-27-2013

Originally Posted by rcgldr

You can use it as an array, even though it's a pointer, for example, v[i].

Ok ok, I did but I get the same error in the function

**rcgldr** · 05-27-2013

Originally Posted by zetaXX

Ok ok, I did but I get the same error in the function

Did you make the previous suggested changes?

You need to make these changes:

Code:

struct Array ArrayCreaAleatorio(int linf,int lsup){
int i;  /* you can't wait until the for loop  for(int i = ... , since this is C and not C++) */
/* ... */
    array1.n = lsup-linf+1;
    array1.v = malloc(array1.n * sizeof(int));
/* ... */

After you make these changes, and if you still have problems, post all of your new code.

**zetaXX** · 05-28-2013

Originally Posted by rcgldr

Did you make the previous suggested changes?

You need to make these changes:

Code:

struct Array ArrayCreaAleatorio(int linf,int lsup){
int i;  /* you can't wait until the for loop  for(int i = ... , since this is C and not C++) */
/* ... */
    array1.n = lsup-linf+1;
    array1.v = malloc(array1.n * sizeof(int));
/* ... */

After you make these changes, and if you still have problems, post all of your new code.

Alright, sorry about taking too long, changes are made, thats my code

Code:

#include<stdlib.h>
#include<stdio.h>
#include<time.h>
#include <malloc.h>


struct Array{
    int n;
    int *v;
};


struct Array ArrayCreaAleatorio(int linf,int lsup){
int i;
int j;
int linf2;
linf2 = linf; 
      struct Array array1;
      array1.n = lsup-linf+1;
      array1.v = malloc(array1.n * sizeof(int));
      for ( i = 0; i=array1.n; i++){
      array1.v[i] = linf2++;
      linf2 = linf2++;
      }


 for ( j = 0; j = (n-2); j++){
     v.array1[j] = (rand()% lsup)+linf;
     }  
     return array1;

And the compiler gives me these errors:
invalid conversion from void* to int*
'n' undeclared (first use this function)
'v' undeclared (first use this function)

**grumpy** · 05-28-2013

You know the old ditty about the hole in the bucket?

The cause of problems in your latest post is the exact same cause as the problems in your original post.

**ZuK** · 05-28-2013

Code:

for ( j = 0; j = (n-2); j++){
     v.array1[j] = (rand()% lsup)+linf;
     }

you have to change v and n here too.
Kurt

**zetaXX** · 05-28-2013

Originally Posted by rcgldr

Did you make the previous suggested changes?

You need to make these changes:

Code:

struct Array ArrayCreaAleatorio(int linf,int lsup){
int i;  /* you can't wait until the for loop  for(int i = ... , since this is C and not C++) */
/* ... */
    array1.n = lsup-linf+1;
    array1.v = malloc(array1.n * sizeof(int));
/* ... */

After you make these changes, and if you still have problems, post all of your new code.

Alright I just needed (int *) between malloc and equal sign, thx!

Thread: problem with structure

Thread Tools

Search Thread

Display

problem with structure

Similar Threads

Problem with Structure inside a structure

Problem Allocating Memory For Structure Within Structure In A Function

Problem writing structure within another structure to file

Problem with do loop in for in my structure in structure program

C structure within structure problem, need help