c - Getting the values of linked list with loops -

i have create function can value of matrix wich take form of double linked list. here structures of matrix

 typedef struct row {     unsigned int indicerow;     struct row * next;     struct col * data; } row;  typedef struct col{     double value;     unsigned int indicecolumn;     struct col * next; } col;  typedef struct matrix{     int nrows;     int ncols;     struct row * rowfirst; }matrix; 

the structure matrix represent top of linked list , contain total number of rows , columns , variable row wich point first node of list of row nodes. row nodes contain number of row of matrice, variable row called next wich represent next line of matrix , variable data point list of col nodes. col nodes contains number of column, value @ coordonates(row,column) , col next. values different of 0 have in col linked list.

to value of precise point of matrix created function sp_get. take structure matrix, line , column i'm looking , double variable argument. returns 0 when works , update variable double *val value i'm looking for.

int sp_get( struct matrix *mat, unsigned int rows, unsigned int col, double *val){         row * temps = (row*)malloc(sizeof(row));         temps = mat->rowfirst;         while(temps->indicerow!= rows){             temps = temps->next;         }          while(temps->data!= null && temps->data->indicecolumn!= col && temps->data->next!=null){             temps->data = temps->data->next;         }          if(temps->data->indicecolumn == col){             *(val) = temps->data->value;         }         else{         *(val) = 0.0;         }          return 0; 

first create row variable run through matrix, row , column. if can't find column means value 0.

when use function 1 value, works well, , return value.(tempmatrix matrix variable , contain linked list)

        double * vall =(double*)malloc(sizeof(double));         sp_get(tempmatrix, 2, 3, vall); 

but when i'm using function double loop don't have same results , can't not explain why...

double * vall =(double*)malloc(sizeof(double));         int i;         int j;         for(i=1;i<=tempmatrix->nrows;i++){             for(j=1; j<=tempmatrix->ncols;j++){                 sp_get(tempmatrix,i,j,vall);                 printf(" %f ", *(vall));             }             printf("\n");         } 

here result loops

and here results should get

it might proble of memory leak, don't know comes from.

thanks in advance help!

just in sp_get alone following problems abound:

memory first 2 lines.

anytime see in successive lines in c:

ptr = malloc(...) ptr = <something else> 

it always memory leak.

updating column header rather enumerating it

once find row seek, this:

while(temps->data!= null &&        temps->data->indicecolumn!= col &&        temps->data->next!=null)     {         temps->data = temps->data->next;     } 

ask yourself, what is temps->data = ... actually updating? changing temps->data pointer point own next, means temps->data pointed prior gone. that's fine if temps->data temporary pointer, but isn't. data member in row struct worked hard find in prior loop.

potential null pointer dereference

you may think having this:

while(temps->data!= null &&        temps->data->indicecolumn!= col &&        temps->data->next!=null) 

for while-condition in loop harbor safety temp-data being null code follows:

if(temps->data->indicecolumn == col) {     *(val) = temps->data->value; } 

but if did, why bother first clause (which correct, btw). appears addition of last clause (temps->data->next!=null) effort stave off crashes. isn't way it.

minor: hiding type col parameter col

needs little explanation. see var names.

minor: there no need dynamically allocate out-parameter you're using it.

your code this:

double * vall =(double*)malloc(sizeof(double)); int i, j; for(i=1;i<=tempmatrix->nrows;i++) {     for(j=1; j<=tempmatrix->ncols;j++)     {         sp_get(tempmatrix,i,j,vall);         printf(" %f ", *(vall));     }     printf("\n"); } 

can this:

double val = 0.0; int i, j; for(i=1;i<=tempmatrix->nrows;i++) {     for(j=1; j<=tempmatrix->ncols;j++)     {         sp_get(tempmatrix,i,j,&val); // note address-of operator         printf(" %f ", val);     }     printf("\n"); } 

---

updated sp_get

i'm pretty sure you're trying do. following return 0 if indexed values found , retrieved, otherwise returns -1 , out-parameter set 0.0.

int sp_get( struct matrix const *mat, unsigned int rows, unsigned int cols, double *val) {     // prime 0.0     *val  = 0.0;     if (!mats)         return -1;      // walk row table     struct row const *row_ptr = mat->rowfirst;     while (row_ptr && row_ptr->indicerow != rows)         row_ptr = row_ptr->next;      // leave if didn't find row.     if (!row_ptr)         return -1;      struct col const *col_ptr = row_ptr->data;     while (col_ptr && col_ptr->indicecolumn != cols)         col_ptr = col_ptr->next;      if (!col_ptr)         return -1;      *val = col_ptr->value;     return 0; } 

note modify nothing in actual matrix, entire thing, including pointers use index within it, can const (and should be).

best of luck.