Thread: returning multiple arrays from one function to another

Looking at your code, the first problem is that all the variables you use in the main are defined in the readinfiles() function.
You must move them outside of the function, for example:

Code:

long double *xx_r;
long double *yy_r ;
long double *zz_r ;

int readinfiles(){
.
.
.
.
	xx_r =  malloc(sizeof(long double) * nrows2);
	yy_r =  malloc(sizeof(long double) * nrows2);
	zz_r =  malloc(sizeof(long double) * nrows2);


}

Originally Posted by giove

Looking at your code, the first problem is that all the variables you use in the main are defined in the readinfiles() function.
You must move them outside of the function, for example:

Code:

long double *xx_r;
long double *yy_r ;
long double *zz_r ;

int readinfiles(){
.
.
.
.
	xx_r =  malloc(sizeof(long double) * nrows2);
	yy_r =  malloc(sizeof(long double) * nrows2);
	zz_r =  malloc(sizeof(long double) * nrows2);


}

ahh ok.. noted: so in fortran, for example, i would do something like the following:

Code:

subroutine readinfiles(xx_d, nrows1,nrows2)
integer, parameter :: N=1000000
real :: xx_d(N)
integer :: nrows1,nrows2

and so on...

.
.
.

return
end

That way all the arrays get passed through the parenthasis.
then in the main program would be :

Code:

program blah
integer, parameter :: N=1000000
real :: xx_d(N)
integer :: nrows1,nrows2

call readinfiles(xx_d, nrows1,nrows2)

so then pass those arrays into:
call nextsubroutine(xx_d,nrows1,nrows2)

So when you say that i have to declare the arrays outside the function - is that delcared in main only?

many thanks!

Originally Posted by laserlight

Agreed, that looks like a problem.


No, that is not required, and in fact is bad advice. Generally, global variables should be avoided. Passing a pointer is likely to be more appropriate.

Hmmm... how would one do that ?

Originally Posted by laserlight

I do not know Fortran so I cannot say if your syntax corresponds to what I have in mind, but if you are talking about the use of function parameters, then yes, that is the right idea.


You should declare the pointers in the main function. You are not declaring arrays at all. Rather, what you can do is then pass a pointer to each of these pointers in the main function to readinfiles as arguments. You would also need to pass pointers to corresponding variables that hold the size of the dynamic arrays.

Looking at your current readinfiles function, I would say that it is doing too much work. You are effectively repeating the same process of reading three times in the same function. Rather, write a function that performs this process once, then pass it different arguments three times.

Ok, thanks for your advice (and everyone else).. i will try to implement this just now and post on my progress....

cheers!

The rule inside a single file is this:

a variable is called global if it's defined outside main() or functions().

If you want to declare them inside the main(), you must then pass all them as function's parameters.

Originally Posted by laserlight

I do not know Fortran so I cannot say if your syntax corresponds to what I have in mind, but if you are talking about the use of function parameters, then yes, that is the right idea.


You should declare the pointers in the main function. You are not declaring arrays at all. Rather, what you can do is then pass a pointer to each of these pointers in the main function to readinfiles as arguments. You would also need to pass pointers to corresponding variables that hold the size of the dynamic arrays.

So against your advice - just so i can get a handle on things - i have done the following which seems to work....

At the top of the program i declare the following...

Code:

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <ctype.h>
#include <assert.h>
#include <sys/time.h>
#include <time.h>
#include "kdtree.h"
#include <fftw3.h>
/* for the read in a csv file code */
#include <string.h>
#define NUM_OF(x) (sizeof (x) / sizeof *(x))
#define MAXLINELEN 256

long double  *xx_d; 
long double  *yy_d;
long double  *zz_d;
long double  *xx_r; 
long double  *yy_r;
long double  *zz_r;
long double  *rad;
int nrows1,nrows3,nrows2;

then in function readin files we have:

Code:

int readinfiles()
{  
.
.
.
	
  xx_d = malloc(sizeof(long double) * nrows1);
  yy_d = malloc(sizeof(long double) * nrows1);
  zz_d = malloc(sizeof(long double) * nrows1);
.
.
.
return 0;

}

finally in int main i write:

Code:

int main(int argc, char **argv)
{	
	
readinfiles();

rr_counts(xx_r,yy_r,zz_r,nrows2,nrows3,rad);  	

.
.
.
return 0;
}

so on the surface it seems to be working fine, but how would you amend this such that i am not declaring global variables? Also, return 0 in the readinfile function seems to not affect things being returned - is this ok?

many thanks in advance!

Originally Posted by laserlight

I had something like this in mind:

Code:

#include <stdio.h>
#include <stdlib.h>
#include "your_other_header.h"

struct Data /* For lack of a better name */
{
    long double x;
    long double y;
    long double z;
};

struct DataList
{
    struct Data *data;
    size_t size;
};

int readFile(const char *filename, struct DataList *data_list)
{
    FILE *file;
    int header_count, line_count;
    int i;

    file = open_file_read(filename);
    if (file == NULL)
    {
        return 0;
    }

    get_file_length(file, &header_count, &line_count);
    data_list->size = line_count - header_count;
    (void)rewind(file);

    /* Assume malloc succeeds */
    data_list->data = malloc(sizeof(*data_list->data) * data_list->size);
    for (i = 0; i < data_list->size; ++i)
    {
        /* Assume fscanf succeeds */
        fscanf(file, "%Le %Le %Le",
            &data_list->data[i].x, &data_list->data[i].y, &data_list->data[i].z);
    }
    fclose(file);
    return 1;
}

int main(void)
{
    struct DataList data_list_d, data_list_r;
    if (readFile("file1", &data_list_d))
    {
        printf("there are %d in FIRST data\n", data_list_d.size);
        free(data_list_d.data);
    }

    if (readFile("file2.dat", &data_list_r))
    {
        printf("there are %d in random data\n", data_list_r.size);
        free(data_list_r.data);
    }

    /* The code for the third file read is left as an exercise for the reader. */

    return 0;
}

Thanks so much for that - it seems to work exactly as you have written it!

cheers
R.

So, one last problem.... I can get the above code to work but i cant see how i 'pass' the x,y & z values into another function...

So, for example, in int main after reading in file to '&data_list_d' i can print to screen the values of x,y,z for data_list_d such that

Code:

for (i=0; i<data_list_d.size; ++i) {
		printf("%d %Le %Le %Le\n"
,i,data_list_d.data[i].x,data_list_d.data[i].y,data_list_d.data[i].z);
	}

but now i want to use those arrays in another function which is called straight afterwards:

rr_counts();

but cant see how to do that.

You must define the function
rr_counts(struct DataList* arrayOne,struct DataList* arrayTwo);

Originally Posted by giove

You must define the function
rr_counts(struct DataList* arrayOne,struct DataList* arrayTwo);

Hi Giove

thanks for the help.. i should probably re-iterate my general ignorance of C syntax.. whilst through this thread i am getting a better handle on structures and pointers, I just need a little push to get over the finishing line.

In the above syntax that you quoted how to pass the arrays through but how does that translate into the following:

1. the rr_counts function itself? what i mean by this is when i delcare the
function what exactly do i put in the paranthasis in terms of

data_list_d.data[i].x,data_list_d.data[i].y,data_list_d.data[i].z

Code:

int rr_counts(how do i pass things in here?) {

do i need to declare anything here?

}

2. In terms of calling the function in int main

Code:

rr_counts(struct DataList* how do i define ArrayOne from say data_list_d.data[i].x ... etc...);

I have tried various combinations but end of with various errors when compiling.

THANKS!
R.