[Solved] How to shrink at runtime a struct matrix (using realloc() for example)

by


  • You should reduce the number of columsn, not rows.
  • Not mat1 but mat1->array should be reallocated.
  • Not nrow and ncol (not updated) but mat1->nrows and mat1->ncols (updated) should be used for the new size.
  • The elements are size_t, so allocating for int mayn’t be enough. Using the variable for calculating size is safe.

In the other words, this part

  mat1->nrows = mat1->nrows - 1;
  mat1->array = (size_t *) realloc(mat1, nrow * ncol * sizeof(int));

should be

  mat1->ncols = mat1->ncols - 1;
  mat1->array = (size_t *) realloc(mat1->array, mat1->nrows * mat1->ncols * sizeof(*mat1->array));

and the part (the 4th line of main() body)

  mat1->array = (size_t *) malloc(mat1->nrows * mat1->ncols * sizeof(int));

should be

  mat1->array = (size_t *) malloc(mat1->nrows * mat1->ncols * sizeof(*mat1->array));

Note that this simple reallocation works only because the matrix has only one row. For matrice having multiple rows, you should move (using memmove or manually) second and later rows to match the new number of columns.

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solved How to shrink at runtime a struct matrix (using realloc() for example)