I'm trying to create and print a matrix, but I'm getting segmentation fault.
int** init_dynamic_matrix (int l, int c);
void print_dynamic_matrix (int** ppints, int l, int c);
int main ()
{
int** ppints = NULL;
int l = 6, c = 3;
ppints = init_dynamic_matrix (l, c);
print_dynamic_matrix (ppints, l, c);
return 0;
}
int** init_dynamic_matrix (int l, int c)
{
int i = 0, j = 0;
int** ppaux = NULL;
ppaux = (int**) malloc (l * (sizeof (int*)));
for (i = 0; i < l; i++)
{
*(ppaux + i) = (int*) malloc (c * (sizeof (int)));
for (j = 0; j < c; j++)
{
ppaux[l][c] = 0;
}
}
return ppaux;
}
void print_dynamic_matrix (int** ppints, int l, int c)
{
int i = 0, j = 0;
for (i = 0; i < l; i++)
{
for (j = 0; j < c; j++)
{
printf ("%d", ppints[l][c]);
}
printf("\n");
}
}
for (j = 0; j < c; j++)
{
ppaux[l][c] = 0;
}
Here's the error: in the first iteration of the outer for loop you will execute this , but ppaux[l] is not yet initialized, so you get segmentation fault.
You probably meant something like:
for (j = 0; j < c; j++)
{
ppaux[i][j] = 0;
}
Because you just created the i-th row of your matrix and you want to se it to 0
Related
I got this but it I can't seem to make it work, tried everything I could think of.
#include <stdio.h>
#include <stdlib.h>
void alocare_vector(int *v, int nr, int elem)
{
int *v1;
if ((v1 = realloc(v, nr * sizeof(int))) == NULL)
{
printf("Memorie insuficienta");
free(v);
exit(EXIT_FAILURE);
}
v = v1;
v[nr - 1] = elem;
}
int main()
{
int a[100][100];
int n, *v = NULL, i, j, k, l, ok = 0, nr = 0;
printf("Number de elements n:");
scanf("%d", &n);
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
scanf("%d", &a[i][j]);
for (k = 0; k < n; k++)
{
for (l = 0; l < n; l++)
{
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
if (a[k][l] == a[i][j] && (k != i && l != j))
ok = 1;
if (ok == 0)
{
nr++;
alocare_vector(v, nr, a[k][l]);
}
ok = 0;
}
}
if (nr > 0)
{
printf("Elements:");
for (i = 0; i < nr; i++)
{
printf("%d ", v[i]);
}
}
free(v);
}
Basically, I need to create a matrix, ans print the elements that appear only once using an array with dynamic memory allocation.
one simple fix is to declare the "int * v" as a global variable and modify the function as alocare_vector(int nr, int elem)
now using a hash table you can store the numbers in the array, below is the your implementation just a bit modified.
#include <stdio.h>
#include <stdlib.h>
int hash[1000]={0};
int * v=NULL;
void alocare_vector(int nr, int elem)
{
int *v1;
if ((v1 = (int*)realloc(v, nr * sizeof(int))) == NULL)
{
printf("Memorie insuficienta");
free(v);
exit(EXIT_FAILURE);
}
v = v1;
v[nr - 1] = elem;
}
int main()
{
int a[100][100];
int n, i, j, nr = 0;
printf("Number de elements n:");
scanf("%d", &n);
for (i = 0; i < n; i++)
{
for (j = 0; j < n; j++)
{
scanf("%d", &a[i][j]);
++hash[a[i][j]];
}
}
for (i = 0; i < n; i++)
{
for (j = 0; j < n; j++)
{
if(hash[a[i][j]]==1)
{
nr++;
alocare_vector(nr, a[i][j]);
}
}
}
if (nr > 0)
{
printf("Elements:");
for (i = 0; i < nr; i++)
{
printf("%d ", v[i]);
}
}
free(v);
}
When calling a your funtion you pass a copy of the pointer. Therfore any modifications to this local copy of the pointer will not affect the copy in main. Therfore you need a refrence or pointer to the pointer in main.
void alocare_vector(int **v, int nr, int elem)
{
...
*v = v1;
}
Here you have brut force example how to generate array of distinct elements of the 2D array:
typedef struct
{
size_t length;
int data[];
}data_t;
data_t *add_element(data_t *arr, int element)
{
size_t newsize = arr ? arr -> length : 0;
arr = realloc(arr, newsize * sizeof(arr -> data[0]) + sizeof(*arr));
if(arr)
{
arr -> length = newsize;
arr -> data[newsize - 1] = element;
}
return arr;
}
int isPresent(size_t rows, size_t cols, size_t vrow, size_t vcol, int (*array)[cols])
{
int val = array[vrow][vcol];
for(size_t row = 0; row < rows; row++)
for(size_t col = 0; col < cols; col++)
{
if(vcol == col && vrow == row) continue;
if(array[row][col] == val)
{
return 1;
}
}
return 0;
}
data_t *distinctElements(size_t rows, size_t cols, int (*array)[cols])
{
data_t *dist = NULL;
for(size_t row = 0; row < rows; row++)
{
for(size_t col = 0; col < cols; col++)
{
if(!isPresent(rows, cols, row, col, array))
{
data_t *tmp = add_element(dist, array[row][col]);
if(tmp) dist = tmp;
else { /* error handling */}
}
}
}
return dist;
}
I need to return the value of the matrix, but I am gettin this error
Subscripted value is not an array, pointer, or vector
in:
qk_output[m][o] = 0;
and
qk_output[m][o] += queries[m][n] * keys[n][o];
Could anyone help me? Thanks!
int* multmm(int queries[M][N], int keys[N][O]) {
// Matrix Multiplication
int* qk_output = (int*)malloc(sizeof(int) *M*N);
for (int m = 0; m < M; m++) {
for (int o = 0; o < O; o ++) {
qk_output[m][o] = 0;
for (int n = 0; n < N; n++) {
qk_output[m][o] += queries[m][n] * keys[n][o];
}
}
}
return qk_output;
}
To return a 2D array from a function, you can do
#define N 4
#define M 3
int (*foo(void ))[N]
{
int (*p)[N] = malloc(M * sizeof *p);
for (int i = 0; i < M; ++i)
{
for (int j = 0; j < N; ++j)
{
p[i][j] = i + j;
}
}
return p;
}
int main (void){
int (*mat)[N] = foo();
for (int i = 0; i < M; ++i)
{
for (int j = 0; j < N; ++j)
{
printf("%d ", mat[i][j]);
}
puts("");
}
free(mat);
return 0;
}
int* qk_output = (int*)malloc(sizeof(int) *M*N);
qk_output is a pointer to an int
the compiler knows how to access qk_output[n] but doesn't know how to access qk_output[m][n], you need to switch to:
int (*qk_output)[N] = malloc(sizeof(*qk_output) * M); // Don't cast malloc
that is, a pointer to an array of N ints
Now the compiler has enough information to access qk_output[m][n]
For the return question: you can use void *multmm(...) or int (*multmm(...))[N], the second one gives more information to the compiler so it is less error prone.
Something like:
int (*multmm(int queries[M][N], int keys[N][O]))[N]
{
int (*qk_output)[N] = malloc(sizeof(*qk_output) * M);
...
return qk_output;
}
int main(void)
{
int (*arr2D)[N] = multmm(...);
...
}
Well i m struggling with the pointers, why doesn t work the function biggest in the end (yes of that s dummy function)? (exit code 6)
Ty for help
code:
int search(int const a[], int n, int key) {
for (int *i = a; i < a + n; i++) {
if ( key == *i ) return 1;
}
return 0;
}
void print_row(int const a[], int n, int row) {
for (int *i = a + n * row; i < a + n * (row + 1); i++) {
printf("%d ", *i);
}
printf("\n");
}
void biggest(double x, long *int_part, double *frac_part) {
*int_part = (long) x;
*frac_part = x - *int_part;
}
main () {
int tempretures[7][24];
for (int *i = &tempretures[0][0]; i < &tempretures[7][24]; i++) {
static int j = 1;
*i = j;
j+=2;
}
tempretures[6][5] = 32;
for (int i = 0; i < 7; i++) {
for (int j = 0; j < 24; j++) {
printf("%d ", tempretures[i][j]);
}
printf("\n");
}
printf("Is it: %d\n", search(tempretures, 7*24, 32));
for (int i = 0; i < 7; i++) {
print_row(tempretures, 24, i);
}
long a = 0; double b = 0;
biggest(5.67, &a, &b);
printf("%li", a);
}
for (int *i = &tempretures[0][0]; i < &tempretures[7][24]; i++) {
static int j = 1;
*i = j;
j+=2;
}
This runs way past the end of the array, stopping only when it hits every element of row number 7, but there is no row number 7.
The title is pretty clear I think.
I am trying to create a program that calculates a 3x3 linear system using determinants, but I am getting a segmentation fault. Here is the code:
#include<stdio.h>
int determinant(int n, int m, int det[m][n])
{
int res;
res = det[0][0]*det[1][1] - det[0][1]*det[1][0];
return res;
}
int main(void)
{
int arr[3][4], det[2][2], i, j, D; //Dx1, Dx2, Dx3
for(i = 0; i < 3; i++)
{
printf("Eisagete tous suntelestes ths %dhs eksisoshs.", i+1);
scanf("%d %d %d %d", &arr[i][0], &arr[i][1], &arr[i][2], &arr[i][3]);
}
for(i = 0; i < 2; i++)
{
for(j = 0; j < 2; i++)
{
det[i][j] = arr[i+1][j+1];
}
}
D = arr[0][0]*determinant(2, 2, det);
for(i = 0; i < 2; i++)
{
for(j = 0; j < 2; i++)
{
det[i][j] = arr[i+1][j+((j == 1) ? 1 : 0)];
}
}
D -= arr[0][1]*determinant(2, 2, det);
for(i = 0; i < 2; i++)
{
for(j = 0; j < 2; i++)
{
det[i][j] = arr[i+1][j];
}
}
D += arr[0][2]*determinant(2, 2, det);
printf("%d\n", D);
}
I am getting the error right after completing the first for loop in main.
In the block:
for(i = 0; i < 2; i++)
{
for(j = 0; j < 2; i++)
{
det[i][j] = arr[i+1][j+1];
}
}
You increment i in both loops, and adding 1 more to it while reading from the array. So at arr[i+1] you are reading to far.
A segmentation fault basically means you are trying to read something you don't have access to.
You shoud never do what you're doing by passing static array sizes m and n as function argument:
int determinant(int n, int m, int det[m][n])
Check https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html for info
#include <stdio.h>
#include <pthread.h>
int arr[1000][1000];
int brr[1000][1000];
int h;
int f;
void *BMM(void *arg)
{
int* neo = (int*) arg;
int ne = *neo;
int sum = 0;
for(int i = 0; i < n; ++i)
{
sum += arr[x][i]*brr[x][f];
++f;
}
printf("%d\n", sum);
crr[x][h] = sum;
pthread_exit(NULL);
}
int main()
{
pthread_t* ar = malloc(3*sizeof(*ar));
printf("Enter the value of m and n\n");
scanf("%d %d",&m,&n);
for(int i = 0; i < m; ++i)
{
for(int j = 0; j < n; ++j)
{
scanf("%d",&arr[i][j]);
}
}
printf("Enter the value of p and q\n");
scanf("%d %d",&p,&q);
if(p != n)
{
printf("The matrix multiplication is not possible\n");
return 0;
}
int* id;
id = (int *)malloc(4*sizeof(int));
for(int i = 0; i < p; ++i)
{
for(int j = 0; j < q; ++j)
{
scanf("%d",&brr[i][j]);
}
}
for(x = 0; x < m; ++x)
{
for(z = 0; z < q; z+=4)
{
f = z;
h = z;
for(int k = 0; k < 3; ++k)
{
pthread_create(&ar[k],NULL,BMM,NULL);
}
for(int k = 0; k < 3; ++k)
{
pthread_join(ar[k],NULL);
}
}
}
for (int i = 0; i < m; ++i)
{
for(int j = 0; j < q; ++j)
{
printf("%d ",crr[i][j]);
}
printf("\n");
}
}
The above program is supposed to multiply two matrix by multiplying row one of matrix by all the columns of other matrix using 3 threads and then row two by all the other columns and so on and then store the respective values int another matrix but it is giving segmentation fault. Where am I going wrong?
I think your problem is here:
pthread_create(&ar[k],NULL,BMM,NULL);
^^^^
void *arg is NULL
and then:
void *BMM(void *arg)
{
int* neo = (int*) arg;
int ne = *neo; // Dereference NULL --> segmentation fault
Further this looks strange:
void *BMM(void *arg)
{
int* neo = (int*) arg;
int ne = *neo; // ne is never used !!
int sum = 0;
for(int i = 0; i < n; ++i) // Where does n come from ?
Perhaps it should be n instead of ne?
If n, x, f and h are global variables you are into trouble as all threads will work on the same variables. That would be real bad. Each thread needs it own variables.
BTW:
Always check the value returned by scanf - something like:
if (scanf("%d %d",&m,&n) != 2)
{
// Add error handling here
}
and
if (scanf("%d",&arr[i][j]) != 1)
{
// Add error handling here
}