c - Field within structure take random values -

i'm new c , i'm trying define matrix using struct , methods change int** field of struct. matrix supposed dynamically allocated , resizable in how many rows can have. when run program below , print out values of matrix in main, matrix have random values, not ones inserted in genmatrix() , addrow(). doing wrong? grateful help.

i define struct this:

typedef struct matrix {     int** matrix;     int rows;     int cols;     int capacity; } matrix; 

and have following methods should change field of struct:

matrix* genmatrix() {     matrix* matrix = malloc(sizeof(matrix));      initmatrix(matrix, 100, 3, 200);      (int = 0; < 10; i++) {         (int j = 0; j < 10; j++) {             int row[] = {i+j, i*j, i-j};                         addrow(matrix, row);         }     }      return matrix; }     void initmatrix(matrix* matrix, int rows, int cols, int capacity) {     matrix->matrix = malloc(rows * sizeof(int*));     (int = 0; < rows; i++) {         matrix->matrix[i] = malloc(cols * sizeof(int));     }     matrix->cols = cols;     matrix->rows = rows;     matrix->capacity = capacity; }  void addrow(matrix* matrix, int* row) {     if (matrix->rows == matrix->capacity) {         matrix->capacity *= 2;         matrix->matrix = realloc(matrix->matrix, matrix->capacity * sizeof(int*));     }      matrix->matrix[matrix->rows++] = row; } 

and in main call function genmatrix , print result out, random values 32691, -1240670624 etc.

int main() {     matrix* matrix = genmatrix();    } 

when try add row here:

        int row[] = {i+j, i*j, i-j};                     addrow(matrix, row); 

the data adding temporary local variable. on next loop iteration overwritten , when loop exits go out of scope.

you need allocate memory new row data, e.g. using malloc:

        int * row = malloc(3 * sizeof(int));         row[0] = i+j;                row[1] = i*j;                row[2] = i-j;                addrow(matrix, row); 

don't forget free these row allocations later when you're done matrix.